Which components is the PCM paired with?
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Which components is the PCM paired with?
I have an SL1, third gen, manual transmission here. A while back it had stopped starting, no fuel pump signal, no fuel gauge, no obd2, and no spark I believe. All the power and grounds to the PCM were ok if I remember right. I'm not 100% that the PCM is busted, but I figure there's a good enough chance it is, and if not it'll help diagnosis to know that it's good.
If I remember correctly the PCM is bound to the BCM and one of those is also bound to the passlock module on the key cylinder. I would either need to program the new pcm, or buy a pcm/bcm/passlock module from the same donor car if I understand correctly. Am I missing anything or is this all correct? I seem to have a 3rd gen donor car lined up with the same transmission type and engine currently. Any other info I'm missing here?
Also big apologies if this has been discussed before. I did a hurried search but didn't find anything close.
If I remember correctly the PCM is bound to the BCM and one of those is also bound to the passlock module on the key cylinder. I would either need to program the new pcm, or buy a pcm/bcm/passlock module from the same donor car if I understand correctly. Am I missing anything or is this all correct? I seem to have a 3rd gen donor car lined up with the same transmission type and engine currently. Any other info I'm missing here?
Also big apologies if this has been discussed before. I did a hurried search but didn't find anything close.
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From: Willamette Valley, Oregon
Sounds like a bcm failure to me but Derf will know for sure. There is a 30 minute relearn procedure to pair up the modules. It requires a charged battery and probably jumpers to a running car.
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Check for fuel pressure on the fuel rail under the hood by putting a rag over the Schrader valve and depressing the center. If you have nothing coming out, and your fuel pump is not running.
What is happening when you try to start the car? Is the engine spinning but there is no firing? Is the security light on the dash solid red or flashing? Do you have spark?
The following is related yet unrelated:
Opn the instrument panel junction box IPJB. Passenger footwell right side of the console down low. Pull off the panel in the same location but on the left side of the console. With the battery disconnected, pull off the back of the internal fuse panel.
There is a certain pin, F5 F4 or F1 depending on the generation of S Car I don't remember which is for gen 3. Several different devices, including the fuel pump, get power from one of the f terminals above. The killer is often the lighter which gets power from the same pin. The lighter was never designed to carry the continuous high current pulled by the current generation of cell phone chargers. It was designed for brief high-current use as a lighter.
If someone has tapped the lighter circuit to put in an aftermarket stereo, and that pulls a significant current, the same thing will happen as that current goes through the same pin.
Basically, the terminal gets too hot, along with the wiring attached to it and the terminal literally melts. Some people have intermittent problems while others it just suddenly disconnects depending on how it melts and how bad. Some people end up with wire insulation melted the plastic behind the PIN. This can usually be cleaned up and fixed. whenever someone tells me there is zilch from the fuel pump and other things that don't work like OBD2, I immediately suspect a melted f pin if the fuses are good. I have never found a decent schematic for gen3 s cars. I'm sure the field service manual has one but I do not have one of those.
You are correct about the key cylinder, BCM, and PCM having to be all on the same page so to speak for the vehicle to start.
However, the system is actually designed with the default security State of inhibit fuel injectors. All of the passlock parameters must match and the BCM must tell the PCM to enable the injectors in order for the car to start and run. It has to keep checking and telling the PCM everything is okay while you. Drive down the road.
Note that passlock kills the injectors, not the fuel pump.
To see if passlock is interfering, when you turn the key to on and crank the car what is the passlock light doing? And what status is it when you release the key from Crank?
If you can get ahold of a decent wiring diagram for the instrument panel junction box oh, you can see exactly what you expect to not work if that if pain goes bad.
Per Andy, search passlock ii reset or BCM relearn. Sometimes passlock gets confused and the signal from the key cylinder never gets to the BCM or it doesn't match because the BCM is confused as to what signal it should receive. Do the long 30 minute reset procedure.
Try the relearn procedure first and follow it to the letter or it will not work. Hook up another vehicle jumper cable style as you will need to leave the Saturn ignition on for 10 minutes at a time three separate times.
If that doesn't work, look at the instrument panel fuse box.
Please let us know what happens
What is happening when you try to start the car? Is the engine spinning but there is no firing? Is the security light on the dash solid red or flashing? Do you have spark?
The following is related yet unrelated:
Opn the instrument panel junction box IPJB. Passenger footwell right side of the console down low. Pull off the panel in the same location but on the left side of the console. With the battery disconnected, pull off the back of the internal fuse panel.
There is a certain pin, F5 F4 or F1 depending on the generation of S Car I don't remember which is for gen 3. Several different devices, including the fuel pump, get power from one of the f terminals above. The killer is often the lighter which gets power from the same pin. The lighter was never designed to carry the continuous high current pulled by the current generation of cell phone chargers. It was designed for brief high-current use as a lighter.
If someone has tapped the lighter circuit to put in an aftermarket stereo, and that pulls a significant current, the same thing will happen as that current goes through the same pin.
Basically, the terminal gets too hot, along with the wiring attached to it and the terminal literally melts. Some people have intermittent problems while others it just suddenly disconnects depending on how it melts and how bad. Some people end up with wire insulation melted the plastic behind the PIN. This can usually be cleaned up and fixed. whenever someone tells me there is zilch from the fuel pump and other things that don't work like OBD2, I immediately suspect a melted f pin if the fuses are good. I have never found a decent schematic for gen3 s cars. I'm sure the field service manual has one but I do not have one of those.
You are correct about the key cylinder, BCM, and PCM having to be all on the same page so to speak for the vehicle to start.
However, the system is actually designed with the default security State of inhibit fuel injectors. All of the passlock parameters must match and the BCM must tell the PCM to enable the injectors in order for the car to start and run. It has to keep checking and telling the PCM everything is okay while you. Drive down the road.
Note that passlock kills the injectors, not the fuel pump.
To see if passlock is interfering, when you turn the key to on and crank the car what is the passlock light doing? And what status is it when you release the key from Crank?
If you can get ahold of a decent wiring diagram for the instrument panel junction box oh, you can see exactly what you expect to not work if that if pain goes bad.
Per Andy, search passlock ii reset or BCM relearn. Sometimes passlock gets confused and the signal from the key cylinder never gets to the BCM or it doesn't match because the BCM is confused as to what signal it should receive. Do the long 30 minute reset procedure.
Try the relearn procedure first and follow it to the letter or it will not work. Hook up another vehicle jumper cable style as you will need to leave the Saturn ignition on for 10 minutes at a time three separate times.
If that doesn't work, look at the instrument panel fuse box.
Please let us know what happens
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Joined: May 2020
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Damn that was a lot. Let me see what I got. I can retest if my battery is still good, but I don't believe I have spark. If I remember my test consisted of holding the end of the plug wire very near my engine to see if I got any arcing. This method worked to test on my honda, but if I'm missing something let me know.
I will check on this pin. I do have an aftermarket stereo, but I'm not sure how it's wired. I do know that I once managed to blow a cigarette fuse that was higher than it was rated for, and I also have run a lighted sign off of that port, so it's possible that it has taken some wear. It however has run since I blew that fuse. I assume if this is the problem the cigarette won't work?
My fuel pump itself runs. if I manually close the relay or short the terminals I can hear it prime. When turning the key and cranking it doesn't activate the relay and obviously, I don't get pump. I also tried cranking while manually running the fuel pump. I do not know if that is safe, but I do know it did not start. I did check for pressure, but I believe I checked after said relay experiment. I did have pressure then. I have also tried swapping the A/C blower and fuel pump relays as they are the same.
My security light is on solid, and I did attempt the relearn procedure at some point. I'm not 100% I did it right, so if I can get my battery charged I may try it again. However, the security light behaves the same with both pcm and bcm removed, so I assume solid doesn't rule out some other failure.
Also, the last time this car ran, I was pulling out of my parking space and the engine sputtered and cut out. It would not start again after that. I have previously had similar sputter (resembling lack of fuel) when the car was a bit toasty. I had also once before had an instance where my car did not start and the fuel gauge was on E when I had gas, however turning it off and on again fixed it. Do these conditions point towards passlock malfunction or something else? I seem to remember reading that passlock won't stop the engine once it's started as a safety measure.
I will check on this pin. I do have an aftermarket stereo, but I'm not sure how it's wired. I do know that I once managed to blow a cigarette fuse that was higher than it was rated for, and I also have run a lighted sign off of that port, so it's possible that it has taken some wear. It however has run since I blew that fuse. I assume if this is the problem the cigarette won't work?
My fuel pump itself runs. if I manually close the relay or short the terminals I can hear it prime. When turning the key and cranking it doesn't activate the relay and obviously, I don't get pump. I also tried cranking while manually running the fuel pump. I do not know if that is safe, but I do know it did not start. I did check for pressure, but I believe I checked after said relay experiment. I did have pressure then. I have also tried swapping the A/C blower and fuel pump relays as they are the same.
My security light is on solid, and I did attempt the relearn procedure at some point. I'm not 100% I did it right, so if I can get my battery charged I may try it again. However, the security light behaves the same with both pcm and bcm removed, so I assume solid doesn't rule out some other failure.
Also, the last time this car ran, I was pulling out of my parking space and the engine sputtered and cut out. It would not start again after that. I have previously had similar sputter (resembling lack of fuel) when the car was a bit toasty. I had also once before had an instance where my car did not start and the fuel gauge was on E when I had gas, however turning it off and on again fixed it. Do these conditions point towards passlock malfunction or something else? I seem to remember reading that passlock won't stop the engine once it's started as a safety measure.
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Joined: Jul 2005
Posts: 12,316
From: Slightly off center
1) Known good battery is Step 0. The electronics in these cars make that a MUST. Otherwise you don't know if anything from your tests are valod.
2) Running ANYTHING extra off the lighter feed -- especially a constant current draw like a sign or stereo -- pulls a static if not increasing current indefinitely. The lighter feed is hot 24/7 so even if your added stereo is off, it's pulling some current for KAM (small) but also some for ?? internally charging capacitors?
You are much better off branching off a new 12V feed of its own, NOT from a pin with other things receiving power distribution. You can run lw enough gauge wire to handle the current straight from the 12V IP BATT input to its own pin then connect to that pin on the otherside of the terminal. I think you should be able to find end connectors that match the pins on the IPJB. Soldering risks overheating and weakening the pin but can be done if your gun is hot enough. Wait until you are sure it works.
3) Spark test -- yes, hold (with insulated handled tool) the metal electrode of connected plug against non painted metal car surface. You should see spark across the gap at regular intervals..
4) Fuel pressure after engaging FP relay = good.
Not starting = bad
FP Relay not engaging on its own = bad without solving this, the vehicle will never "run."
5) Solid Security light + wacky dashboard = passlock "engaged" and likely BCM issues -- but we may be able to overcome this.
6) Security light w no bcm or pcm -- never had anyone try that --- good to know the result is nonsensical -- gotta love GM
7) getting spark is critical but if you can't get fuel from the pump it doesn't help much. Based on your description, it may be a failing/failed crank position sensor (CKP). When this fails on an S car, it cuts fuel and spark to keep the engine from firing without knowing where things are in the engine rotation, Pain to get to, but should be 500 700 ohms cold. They intermittently fail hot and will read open circuit when failed (coil inside has complete break in it.
Do you remember the last time it ran if the security light was solid or flashing after you started it, and if the gauges were wacked out before it sputtered?
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So the car won't run with Passlock tripped
The car won't run w/o the FP relay properly triggered properly
The car won't run w/o/ spark
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A) would check to see if it involves a IPJB F piin issue involving the fuel pump relay. I'm betting OBDII comes off the same pin.
If you can get OBDII functioning again, we should be able to pull some codes (PCM and BCM reinstalled of course).
I'll look at older 2nd gen wiring diagrams for a guess at what's wired to which pin. I've never owned a 3rd gen -- they are the only S cars to have BCMs. I do not know if the BCM triggers the FP relay or if it is tired to the ignition cyl circuitry like it was on the 1st n 2nd gen S cars.
See if there is anything melted or smoked in the IPJB while I dig for some schematics.
While it is true the BCM drives the dash, if part of the IPJB is burned up, some of those signals may be hosed feeding INTO the BCM if there is wiring damage (hopeful thinking).
Only one way to find out.
Step 0: KNOWN GOOD BATTERY--- repeatedly dead, recharged, and won't hold 12.6V overnight does not count
2) Running ANYTHING extra off the lighter feed -- especially a constant current draw like a sign or stereo -- pulls a static if not increasing current indefinitely. The lighter feed is hot 24/7 so even if your added stereo is off, it's pulling some current for KAM (small) but also some for ?? internally charging capacitors?
You are much better off branching off a new 12V feed of its own, NOT from a pin with other things receiving power distribution. You can run lw enough gauge wire to handle the current straight from the 12V IP BATT input to its own pin then connect to that pin on the otherside of the terminal. I think you should be able to find end connectors that match the pins on the IPJB. Soldering risks overheating and weakening the pin but can be done if your gun is hot enough. Wait until you are sure it works.
3) Spark test -- yes, hold (with insulated handled tool) the metal electrode of connected plug against non painted metal car surface. You should see spark across the gap at regular intervals..
4) Fuel pressure after engaging FP relay = good.
Not starting = bad
FP Relay not engaging on its own = bad without solving this, the vehicle will never "run."
5) Solid Security light + wacky dashboard = passlock "engaged" and likely BCM issues -- but we may be able to overcome this.
6) Security light w no bcm or pcm -- never had anyone try that --- good to know the result is nonsensical -- gotta love GM
7) getting spark is critical but if you can't get fuel from the pump it doesn't help much. Based on your description, it may be a failing/failed crank position sensor (CKP). When this fails on an S car, it cuts fuel and spark to keep the engine from firing without knowing where things are in the engine rotation, Pain to get to, but should be 500 700 ohms cold. They intermittently fail hot and will read open circuit when failed (coil inside has complete break in it.
Do you remember the last time it ran if the security light was solid or flashing after you started it, and if the gauges were wacked out before it sputtered?
--------
So the car won't run with Passlock tripped
The car won't run w/o the FP relay properly triggered properly
The car won't run w/o/ spark
----------
A) would check to see if it involves a IPJB F piin issue involving the fuel pump relay. I'm betting OBDII comes off the same pin.
If you can get OBDII functioning again, we should be able to pull some codes (PCM and BCM reinstalled of course).
I'll look at older 2nd gen wiring diagrams for a guess at what's wired to which pin. I've never owned a 3rd gen -- they are the only S cars to have BCMs. I do not know if the BCM triggers the FP relay or if it is tired to the ignition cyl circuitry like it was on the 1st n 2nd gen S cars.
See if there is anything melted or smoked in the IPJB while I dig for some schematics.
While it is true the BCM drives the dash, if part of the IPJB is burned up, some of those signals may be hosed feeding INTO the BCM if there is wiring damage (hopeful thinking).
Only one way to find out.
Step 0: KNOWN GOOD BATTERY--- repeatedly dead, recharged, and won't hold 12.6V overnight does not count
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Sorry I'm late..
I hooked her up to a charged battery, and went over the steps. The security light doesn't turn off after the 10 minutes, or 12 minutes, or 15 minutes....
I went ahead and tried just waiting 12min each time, but no luck...
I don't know what to think of this thing...
Everything on the IPJB looks ok, but i haven't probed anything. No burn marks or melted stuff. idk if it makes a difference, but my cigarette port is working also. I'll look into rewiring the light if I get her running. There's a large gauge wire that runs from the battery to the amps in the back that I could tap into.
I checked the crank sensor, it reads 800ohms at the pcm connector... is that an issue?
As far as the dash gauges, I'm pretty sure they worked that morning, I would have most likely freaked if they didn't. I really don't remember about the security light, but I have slightly older pics of the dash on with the security light off, so I'm guessing it was probably off before...
As far as the security lamp being on with no computers installed, I tried that because I wanted to know if the security light was conclusive proof that the passlock was engaged, or if it could also mean total failure of the computers. Also interesting, if I remember correctly, the ODO still displays correctly with the computers out if I remember right...
I haven't looked at any diagrams yet, but I'll get to it soon.
I hooked her up to a charged battery, and went over the steps. The security light doesn't turn off after the 10 minutes, or 12 minutes, or 15 minutes....
I went ahead and tried just waiting 12min each time, but no luck...
I don't know what to think of this thing...
Everything on the IPJB looks ok, but i haven't probed anything. No burn marks or melted stuff. idk if it makes a difference, but my cigarette port is working also. I'll look into rewiring the light if I get her running. There's a large gauge wire that runs from the battery to the amps in the back that I could tap into.
I checked the crank sensor, it reads 800ohms at the pcm connector... is that an issue?
As far as the dash gauges, I'm pretty sure they worked that morning, I would have most likely freaked if they didn't. I really don't remember about the security light, but I have slightly older pics of the dash on with the security light off, so I'm guessing it was probably off before...
As far as the security lamp being on with no computers installed, I tried that because I wanted to know if the security light was conclusive proof that the passlock was engaged, or if it could also mean total failure of the computers. Also interesting, if I remember correctly, the ODO still displays correctly with the computers out if I remember right...
I haven't looked at any diagrams yet, but I'll get to it soon.
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From: Slightly off center
Started to reply to this but lost it.
Knowing that passlock light is on solid with no computers installed doesn't tell us anything useful since we don't know the logic associated with the wiring, though I would think that it would be wired to be normally on until BCM opens the circuit when passlock is off.
Solid passlock security light +:whack gauges + no spark + fuel relay never triggered
=. BCM failure in the absence of other potential problems.
As far as replacement goes you can get a matching PCM and BCM from a donor car. I believe a new passlock cylinder can be married to the BCM at the same time the PCM is married to the PCM.
if you want all your options to function properly, you need to find a donor BCM from a vehicle that is essentially identical to yours in terms of options. This is possible but usually not simple.
Another option is keeping your PCM and having a GM dealership sell you a refurbished BCM and charge you to program it to match the VIN of your vehicle. They will not reflash a junkyard unit. Potential issues with odometer fraud even though it sounds like this vehicle stores it in the cluster. I guess you could ask. Flashing a refurbished BCM to match your VIN guarantees in theory that all you are options will work.
I cannot guarantee your PCM is not defective. Since he will have to pay for a diag at the dealership, have them test to see if the PCM is still good. It should be. If it is not, you may want to ditch all of this.
Sorry for the bad news
Knowing that passlock light is on solid with no computers installed doesn't tell us anything useful since we don't know the logic associated with the wiring, though I would think that it would be wired to be normally on until BCM opens the circuit when passlock is off.
Solid passlock security light +:whack gauges + no spark + fuel relay never triggered
=. BCM failure in the absence of other potential problems.
As far as replacement goes you can get a matching PCM and BCM from a donor car. I believe a new passlock cylinder can be married to the BCM at the same time the PCM is married to the PCM.
if you want all your options to function properly, you need to find a donor BCM from a vehicle that is essentially identical to yours in terms of options. This is possible but usually not simple.
Another option is keeping your PCM and having a GM dealership sell you a refurbished BCM and charge you to program it to match the VIN of your vehicle. They will not reflash a junkyard unit. Potential issues with odometer fraud even though it sounds like this vehicle stores it in the cluster. I guess you could ask. Flashing a refurbished BCM to match your VIN guarantees in theory that all you are options will work.
I cannot guarantee your PCM is not defective. Since he will have to pay for a diag at the dealership, have them test to see if the PCM is still good. It should be. If it is not, you may want to ditch all of this.
Sorry for the bad news
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