Hi everyone,

Thank you in advance for your help with this, and for even reading this. I am trying to troubleshoot my car on my own. (It's a 2003 L300.) It broke down right near my house on the way home, and has been sitting in my driveway ever since. I'm not in a position to have it towed to a garage for a mystery diagnosis (unless it really comes to it), but I think I have an actionable theory that I want to run by a friendly expert or two before I plunk down the $300 for a new PCM.

I ran the codes and will list them below. But before it broke down, it was showing multiple check engine lights, seemingly randomly. First one for a while, then a second, and eventually three different lights, each with a slightly different pic of an engine. One would be on for a while, then two, then neither of those and the other one would be on instead, etc. No changes in the car behavior or performance otherwise during this time. It was a few weeks with the one check engine light, and maybe a couple more weeks with the random variety trio. I got an oil/fluid change somewhere in there and that didn't change anything.

Anyway, finally on the way home one day it was running spotty, and then gave out, and wouldn't restart. (Or would start for a second and then die.) One of the relays under the dash was buzzing after it died, so my first guess was to replace that, but that didn't change anything. I gave up for a while after that, and then finally got my hands on a code reader a while back. And to my very amateur eye, they seem to point to a likely suspect (the PCM), but since it's ~$300 to order a new one online, I wanted to get a more knowledgeable opinion.

Below are the (many) OBD2 codes I got, along with the basic summary of each from troublecodes.net. Two main things make me think the PCM (and/or TCM?) are the problem:
--First, under the "possible causes" section on troublecodes and elsewhere, "PCM [or TCM or ECM] has failed" was one of the possibilities listed for many of the codes, and almost all the rest are about those modules getting bad readings.
--Second, a number of the codes contradict each other. (System voltage high / system voltage low; high input / low input; stuck on / stuck off, etc) Others describe things that were not happening (like the one that says I was going 185 MPH)

Those combined with the randomness of the check engine lights coming and going (alongside no performance problems), and the fact that the codes seem to describe a car having all sorts of different failures, while mine seemed to be running fine until the very end, make me strongly suspect that the PCM has basically lost its mind. Does that theory seem to make sense? Also, could the PCM failing result in the TCM giving bad data and appearing bad too? Or do they often go down together? (My understanding is the PCM and ECM are combined in this model, but TCM is a separate unit.)

Thanks again for any help! I'm so tired of having my car stuck here! :-\ (Also, thanks in advance for not telling me I should have checked my engine when the lights told me to. I'm already with you there. :-))

-Lance

(In the list below, the ones with asterisks ** had either ECM, PCM, or TCM failure listed as one of the possible causes in my research.)

P1887 Torque Converter Clutch Release Switch Circuit Malfunction **

P1860 TCM PWM Solenoid Circuit Malfunction When the PCM detects a continuous open, short to ground or short to voltage in the TCC PWM solenoid valve circuit, DTC P1860 sets. p1860 is a more wide capture code of solenoid problems. **

P1847 Crankshaft Position Sensor B Circuit Malfunction. or 2-3 Shift Solenoid Circuit High Input Voltage **

P1845 2-3 Shift Solenoid Circuit Low Input Voltage (Torque Limit Management)

P1843 A/T 1-2 Shift Solenoid Circuit High Input **

P1842 A/T 1-2 Shift Solenoid Circuit Low Input **

P1834 Torque Converter Clutch (TCC)/Shift Solenoid (SS) Control Circuit High Voltage

P1833 A/T Pressure Control Solenoid Circuit High Voltage **

P1832 Pressure Control (PC)/Shift Lock Solenoid Control Circuit High Voltage (The TCM detects an internal short to voltage on the high side driver 1 circuit for 0.3 second or greater of a 0.5 second sample.)

P1831 Pressure Control (PC)/Shift Lock Solenoid Control Circuit Low Voltage (The TCM detects an internal open or short to ground in the high side driver 1 for 0.3 second or greater of a 0.5 second sample.)

P1818 Transmission Fluid Pressure (TFP) Valve Position Switch Indicates Drive without Drive Ratio (The TCM detects a PARK, NEUTRAL, or a drive range with a REVERSE ratio for 3 seconds.)

P1817 TFP Valve Position Switch Circuit Malfunction **

P1816 Transmission Fluid Pressure (TFP) Valve Position Switch Indicates Park/Neutral (P/N) with Drive Ratio (The TCM detects P/N with a drive ratio for 6 seconds.)

P1815 TFP Valve Position Switch Circuit Malfunction **

P1810 Transmission Fluid Pressure (TFP) Position Switch Circuit (The TCM detects an invalid gear range for 60 seconds. The TCM detects an invalid TFP manual valve position switch state for 5 seconds.)

P1791 Throttle Pedal Position Signal Malfunction **

P1621 PCM Memory Error

U2105 Lost Communication With The ECM

P0757 Shift Solenoid (SS) 2 Valve Performance - Stuck On (The TCM detects shift solenoid valve 2 is ON when commanded OFF.)

P0756 2-3 Shift Solenoid (SS) Valve Performance - No First or Second Gear

P0752 Shift Solenoid (SS) 1 Valve Performance - Stuck On

P0751 1-2 Shift solenoid (SS) Valve Performance - No First or Fourth Gear

P0742 Torque Converter Clutch (TCC) System - Stuck On

P0741 TCC System Mechanically Stuck Off

P0727 Engine Speed Circuit Low Input **

P0717 Input Speed Sensor Circuit Low Voltage

P0716 Input Speed Sensor Performance

P0603 Control Module Random Access Memory (RAM) The ECM detects an internal failure or incomplete programming for more than 10 seconds **

P0602 Control Module Random Access Memory (RAM) The ECM detects an internal failure or incomplete programming for more than 10 seconds. **

P0601 Control Module Torque Performance (Voltage and ground inputs to the ECM; High resistance, short or open condition to the ECM; ECM is not properly programmed) **

P0563 System Voltage High - ECM (The ECM detects that the system voltage is greater than 16 volts.)

P0562 System Voltage Low (The HPCM detects system voltage is 10 volts or less for 5 out of 6 seconds.)

P0503 Vehicle Speed Sensor Circuit Intermittent (The ECM detects the vehicle speed is greater than 300 km/h (185 MPH) for greater than 1 s.)

 

Welcome, what year is your L300. There are two series of these cars, 2000-2002 and 2003-2005. 2004 can have either engine so if it is a 2004, please specify. I bought my latest LW300 with what turned out to be a bad pcm.

 

I'm so sorry - it's a 2003. I'll edit the original post to include that. Thanks!

 

There is a new member area where you can enter your information, then come back here for mechanical help. I have a set of factory service manuals. I found that my scanner did not even see the pcm on my car. The dash was crazy looking for the pcm. My scanner found the bcm, and the tcm. The car was full of codes, had good compression but no joy.
How many miles on your car? When was the timing belt replaced? Did the transmission work properly before the current issues?

 

Andy,

Can the communications failure U code lead to situations like this where it rains transmission codes and other things when the ECM loses communications with some other major module or modules? I don't expect all of these codes to be due to something like that, but if the transmission wiring harness came loose, the interpretation by the PCM of that might be quite interesting.,.

 

To have a starting point. Clear all codes. Turn key on but no start. Record any KOEO codes. Start engine and allow to idle for at least 1 minute. Did any new codes set? Drive it for a short trip. Any new codes.
Report your findings and we can establish a proper approach to repair.
I'm assuming this vehicle starts. If not clear the codes and see what sets with key on.

 

Hi - thanks for your help. The car does not start. It would turn over and seem like it might, but never quite catch.

I also don't have the code reader anymore (it was a loaner). But I did clear out the codes before both of the times I got readings. Two separate times, about a week apart. The second time had a lot less codes than the first, but I think I just found a different spot with more codes the first time. (The pics I have of the first session show one set of 20 codes, plus another set of 14. The second batch of pics just has the set of 20, identical to the first round's 20.)

It's possible that batch of 14 was some leftover stuff I guess. This was my first time using a code reader. Just for clarity, these are the 20 that I got both times:
P1845
P1843
P1942
P1834
P1833
P1832
P1831
P1810
P1791
P1621
U2105
P0741
P0727
P0716
P0603
P0602
P0601
P0563
P0562
P0503

And this is the other batch of 14 (which has one in common with the other batch):
P0716
P0717
P0742
P0751
P0752
P0756
P0757
P1815
P1816
P1817
P1818
P1847
P1860
P1887

Thanks - sorry I don't have more to work with! Just looking for the best educated guess based on the evidence at hand. Though the replacement PCM is ~$270, I can return it if need be and will just be out shipping + a $85 programming fee. So the gamble is really just about $100 and some hassle, but I still wanted to find someone who knows things who thought it was a reasonable-to-likely possibility that the PCM might be dead. My two mechanical buddies in real life are both old school and know not of PCMs. :-(

 

Not much direction there. Some of those codes are set under driving or engine running conditions so we need to start from scratch.
A simple code reader is cheap. I'd opt for a scanner For under 200 it'll pay for itself quickly.

 

To get started on a no start we need a scan tool. You are going to want/need one.