Engine power reduced and a plethra of codes
 

New to me 08 Aura with the 3.5L and 176k. It had a cracked radiator so I replaced it along with the cooling fans and overflow tank as it was leaking from the bottom. Car ran just fine for an hour drive. cleaned the MAF with MAF cleaner and went to get gas the next day and filled it up, started the car and immediately got hit with reduced engine power, service esc, service tpms,. Pulled codes and got P0641,0106, 0107,0452. Im new to GM and have no idea what im looking for. Ive checked for crunched wires and made sure the terminals on the batt were good. Any help would be appreciated.

1) I'll describe the codes in a second. First of all, check to make sure that the MAF sensor wiring got plugged back in firmly when you were finished cleaning it. Also, very carefully inspect the wiring pigtail connector for breaks in the wiring. Trace the wiring back to where it joins the nearest harness.

This one is kind of odd because this engine has both a MAP and a MAF. You stated you cleaned the MAF, but two of the codes are specific to the MAP.

Might you have unplugged the MAP pigtail and forgotten to reattach it?

Basically, sensors are connected to receive a 5 volt reference signal from the ECU and then respond with an output voltage that is usually something lower than 5 volts. These 5v references sent to the sensors are connected in parallel with each other So if one of them does not get the five volt signal, it means there is a break in the 5 volt circuit or one of the sensors is malfunctioning and one or more sensors are not receiving the required reference voltage. The ECU interprets this as an open circuit.

Many times it takes a few key on key off cycles for the ECU to decide if funky data it has collected is real or just a fluke. You probably hit the number of keyons to set the codes as opposed to them being considered pending.

One of the MAP codes states the response voltage is below the acceptable minimum voltage.

Hence my first thought is that you unplugged the MAP and forgot to plug it back in.

Please check your work and let us know.
We've all done it....
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I'll recheck the wiring today and see. I never unplugged the MAP but it is very loose sitting up there. I also just think it's strange this happened after getting gas. One of those codes is for EVAP, do you think the fill up sent the pressure sensor out too?

Without knowing what sensors are connected in what order on which bus as there are multiple buses, it's impossible to tell right now. I don't have any literature on the aura so I don't know how things are wired.

I have a hard time believing getting gas would cause a pressure sensor failure, but anything is possible. Did you feel past the initial click off of the pump? You really can't do that these days as gas ends up in vacuum lines as a liquid where it's supposed to be vapor. I suppose something like that would screw up the pressure reading if it were to occur. Again that is all speculation.

If you have a scanner that has enough capability to look at the pids, you can likely check and see what that pressure sensor is reading. Same with the MAF and same with the MAP. Since they are p codes, I believe you would find them as pids under the standard OBD2 pids as opposed to manufacturer's codes. But your scanner has to be able to display real time data.

I was hoping for a simple fix before going this route. They always check the last thing you did approach.

You will probably need a wiring diagram to figure out which wire is the 5 volt reference going to all these sensors, but if you can discern which sensor is misbehaving, you can avoid back probing all that stuff. Hopefully. Plus that signal is critical to the operation of many many things so it's best not to perturb it unless you have to or the 5V wiring to a sensor is actually the problem.

​​​ I always leave evap codes last when diagnosing unless I have reason to believe it is the direct cause. A wiring diagram is pretty much critical in this case to see what order the sensors are connected. You can make up for that with the real time data check in terms of what is not functioning properly
But then the question comes down to is the component or sensor itself the problem or is it not getting the reference signal....

Where are you located? I'm unemployed and bored.

I live in Oklahoma City. So I rechecked all the plugs and they are secure. Checked for the 5v at the MAF and MAP. The MAF shows 5v but the MAP shows 1.5 from the plug. So I'm assuming the wiring to the MAP might me messed up somewhere. Sounds like a headache tracing wires. Also my OBD keeps disconnecting and it won't let me clear the codes. I wonder if that's a fuse?

https://cimg7.ibsrv.net/gimg/www.sat...cd75430f6b.jpg
Here's what I've got for the cods as of now

You didn't mention the other three were pending but they will very likely become official codes.

Again we are going to need a schematic to figure out the 5 volt reference signal path to each of the sensors on the A circuit

Hopefully someone will chime in with one, if not I'll have to check ebay to see if i can fine a work manual. Thanks for your help so far

I'm sure it's out there. Just need to search for the 5v ref schematic

Found this. 2008 aura but with the 2.4. not sure it is correct for the 3.5 but I can't see the wiring being conceptually different.

THe picture is very low resolution so if you expand it it is even harder to read. Probably easier with a magnifying glass.

First, the sensors received 5 volt references in parallel, not in series which is what I thought but not what I read. I'll go back and fix that.

From the diagram the fuel tank pressure sensor, MAP, and apparently the throttle position sensor A share a 5 volt reference signal.

The low map voltage code would imply that the map may not be getting the five volt reference.

The EVAP code for the fuel tank pressure sensor would also possibly indicate the same is true for that sensor. One should not affect the other. I'm surprised you did not get a throttle position sensor code.

So now that we have confirmed they are on the same reference circuit, you are going to have to read real time data or measure the 5 volt reference signal at or near the sensor. I believe the fuel pressure sensor is mounted on top of the tank which is a pain in the ass but if you can backprobe the wires leading up to it....

Come to think of it, you are in limp mode. This is often triggered when the two throttle position circuits do not return the same throttle position measurement to the ECU. Per the diagram it is possible that a portion of your ECU is damaged and is not putting out the 5 volt reference signal to those sensors in the diagram.

Time to get out the voltmeter and check the reference voltage lines.

Can't upload the picture because it is in some whack file format that the forum will not accept

Yeah I figured I would have to get in and start probing wires to see. Today I went out there and started it, and kind of pulled on the wires coming off the MAP, and it would sputter, then idle normally, but still in low power mode. Unplugging the MAP had no effect so im leaning toward the wiring being messed up going there.Of course the EVAP would be on top of the tank after I filled int up.As far as the ECU goes I have a workshop manual coming, should be here by next week. Ill check the lines from there once I get it and update you. I gotta take a break from this car for a minute before I break something out of frustration.

At least you didn't get one of them (Aura) that had a defective brake switch. On those cars, the brake lights were on whenever your foot was not on the brake. They turned off when you hit the brake pedal.

Can't believe there were not more accidents

Those cars are known for having electrical system Gremlins. Don't really know much more than that.

Keep in mind that it may be something as simple as corrosion on the sensor pins or the pigtail contacts. Start simple.

The factory scanner is very nice even compared to the latest Snap-on model. Didn’t mean to threadjack your Aura thread. It is just that these newer cars are so complicated with many computers talking over high speed networks. My 2020 and newer Fords have four high speed CAN networks and two medium speed networks. I am constantly in the factory repair website learning the new systems that apply to our trucks.

My repair manual came in and i think ive found what we were looking for.
https://cimg9.ibsrv.net/gimg/www.sat...b62d6f5ce2.png

I fixed a three source v-ref Ford Diesel today. All the sensors on the “b” 5 volt feed were throwing codes and derating the engine. I started with the most likely sensor on that feed. I ran through the tests on the exhaust pressure sensor and it failed the test. Anything in the exhaust stream seem to fail easily especially pressure sensors. I still had four permanent codes that will only clear after an OBD 2 test drive with no problems. My truck passed it’s test drive and came back with no codes stored or pending. Back to work for you!
I see that your car uses two feeds to the accelerator pedal for a nice redundancy. You can still limp home if one feed fails. The manufacturers are getting smarter at our expense. A failed sensor can kill the whole 5 volt circuit. Look at every sensor on the side with the codes. Start with the pressure sensors and see if they are out of range. The car may come back to life with the failed sensor disconnected.

Andy,
There are dotted lines external to the BCM and ECM in the schematic. They appear to externally connect pins on either the 5V or GND independent of what is connected to the pins between them. Like external jumpers.
Is this for monitoring purposes? To monitor the voltage at specific pins where the difference in voltage should be zero if all is well? Or are these simply redundant connections as a fail safe for certain sensors?

Also, the individual sensor wiring is marked X1 or X2 at the top/bottom of the wiring that runs from the five volt rail and the gnds respectively. The signals from the BCM are labeled as 5V1 and 5V2.
They can't indicate which reference voltage they are receiving as that is indicated by the diagram itself. Communications designation??

Notwithstanding, said dotted lines seem to bridge 5v1 and 5v2. If this is actually the case, the two voltage sources are not independent and it seems as though it would make it more difficult to troubleshoot, unless you are using the absence of 5 volts on the high side of a sensor that is located between 2 5 volt sources as your criteria for finding open circuits along the 5 volt and ground rails respectively.

If a sensor completely burns up and goes open circuit, that would not be detectable by looking at its 5 volt source pin vs ground. If it becomes a dead short, that's a different story.

A brief explanation of circuit design here would be most appreciated.

From that drawing it looks like x1 and x2 are the connector references. The numbers are pin locations in those connectors. Most of the Ford sensors I deal with have three wires. V-ref, signal return and a value. Looking for a voltage drop.

so i pulled the fuel line under the hood to siphon the tank to almost empty in case I have to drop the tank, then ran live data. I cleared the codes and the code for the traction contol and whatnot, and the car ran just fine until I hit a crest on my street, then it went back to previous performance. EVAP looks to show 0 so Im leaning toward that EVAP sensor on top of the tank giving me all this grief


https://cimg0.ibsrv.net/gimg/www.sat...cf8b96d74a.png

You mean fuel pressure sensor, yes?

Do not run your vehicle with almost no fuel in the tank. The fuel pump uses the gas around it as a heat sink. Generally you want to keep a minimum of 1/4 tank to keep the entire fuel pump submerged in gasoline. Otherwise, you are letting the pump heat up which will likely shorten its life. I know this is a special case for testing. Just saying in everyday life not to do this if at all possible.

Yeah that. And I know i don't ever run my cars low on gas. It's barely under a quarter but I wanted to recreate the environment it had before it stopped running right and also prep for tank drop.

I thought it was much closer to empty. But we are on the same page anyway 🙃

It'll be a few days before I'm able to dig back into the car but as soon as I do I'll update y'all on progress

Thx x x

p0641
 

Were you able to find the cause of the P0641? My daughter’s Aura 2.4 is showing the P0641 code and wondering what to check first.

It would appear not