When I put the paperclip between 4 an 12 on the OBD, then I get C41 on the speedometer. According to my knowledge that is the C41 in this topic.

I just don't get any codes when shorting the 3 and 4 pins in the OBD-I plug.

 

To save a lot of time I'd recommend fully ensuring vats is sorted out before diagnosing the car further. Sounds like the starter is bypassed but vats still has the fuel injectors disabled which is why the car runs when you spray fuel in the intake. It's very likely this is your issue as C41 errors frequently still allow the car to run.

Pins 3 and 4 are for the FX3 Selective Ride Control module, you can disregard those.

I'd unplug the ECM drivers side under the hood and open it up to check for water damage, they aren't 100% waterproof. If it wasn't replaced I would highly suspect that's your issue in regards to the C41 error. Would be good to then check the tan CKT800 ground wires before to rule them out before replacing the ECM. The Factory Service Manual shows a diagram of all the CKT800 ground locations, check each one starting with the transmission ground and make sure their all ground. Search info on 94-96 ECM/PCM swaps if that seems to be the last option at fixing the issue.

 

The VATS isn't bypassed per se. I just cut the wire from the ignition and added a resistor that matches the key (there were issues with the key resistor). Before that the security light stayed on, but now it is off (or blinking, when the door is open). For that reason I have ruled out the VATS.

Great (Y).

I have my doubts about the ECM, but I am not 100% sure... I will concider opening the ECM, but I will leave it as a last resort before replacing the ECM.
I have the FSM, but I can't find any reference to the CKT800 ground locations. I have the Chiltons FSM, if it says anything. If someone could point out the ground locations, then that would be awesome. Especially the transmission ground.
What I do know, is that neither of the CKT800 wires on the ECM have a contact with ground (no continuity between the negative battery end and neither D29 nor D30 on the blue ECM plug). Should there be a continuity at one of them to ground (negative end of the battery or frame of the car)?

Thank you in advance,
P6tu

 

C41 code causes are very complex, most occur while the car is still drivable. I solved mine by replacing the ECM as it had failed. The car ran fine even though it couldn't read codes from the ECM. You have to search for the CKT800 locations as they are slightly different for each specific year. Aftermarket stereo's can cause C41 codes, so can a single blown fuse or burned out or corroded ground can cause it. Failed ECM's are common even though the car continues to run. If the injectors aren't firing I'd be even more suspicious of a failed ECM.

Heads up, if you open your ECM make sure to do it indoors away from the sun and fluorescent lights. The swappable Memcal EPROMS are UV light erasable which contain the car's year specific calibration data.

 

Why would a communication wire between the CCM, ECM, ABS, HVAC, and Radio be grounded anywhere?

 

No, aftermarket radio will cause a 72 or 74. Not a 41. There is even a TSB for it

His ECM is quite different from your 90. There is no swappable EPROM inside.

 

CKT800 ground wires.

 

Please do tell where it shows 800 being grounded, much less grounded to the bellhousing.

 

CKT800 short to ground. If you read my OP from 2018 you can see I refer to them correctly, serial communication and grounds.

Depending on how the stereo was installed, (subs, amps etc) has been linked to C41 codes. Electrical noise alone can disrupt the "dated" serial communication between modules and good to rule out.

Totally correct about 95 not having EPROM's in the ECM, 94+ have to be programmed and instead have ESCM's that need to be swapped out instead. Likewise, when opening any module it's good practice to do it away from UV sources.

Keep it coming.

 

Hello,

So a little update to this ongoing thing. Finally had some time to deal with the car and now I ran into another issue - I can't start the car because I can't get it out of gear. Since the shifter boot frame was bad, then I "glued" it to the plastic frame and while dismembering the center console (to remove the aftermarket radio) I shifted the lever to 2nd. Now I wanted to shift it back to P or N, but I was not able to do it. Videos of the issue (Youtube): , . Not sure, why the first video was uploaded as a short thing or something. Also some pictures of the linkage at the shifter:

Shifter lever as it is with the top cover in place.

Top cover removed and the current position of the lever linkage underneath.


PS! If this is too offtopic, then I don't mind, if this is move to another thread... Root problem is still the same C41 - just a temporary setback...

 

---- delete the post ---- double post ----

 

Where does the CKT800 go throught the firewall? I am a bit confused about that part. I can't even see a reference to that in the ECM serial data circuit. All the other points seem to be described (like WD12 and WC13)...

 

That shifter problem could be a number of things, guessing the shifter release solenoid however it's outside the scope of your CCM 41 error so please repost it in a separate thread under C4 tech/performance section so we can focus on your CCM 41 issue.

As for the 800 tan colored wires they have different locations depending on the modules and each model year. You need the electric supplemental service manual for your specific year. Reference the tan wires based on the pin out locations on the CCM and ECM then follow them back from the modules. They go behind the stereo area and under the driver dash to terminal M on the ALDL connector. Don't open or disturb the loomed harnesses as they are old and brittle at this point and this can cause all sorts of additional issues. Disconnect the battery and simply follow the looms back where they route from the modules themselves then I would do continuity and resistance checks between all points and also terminal M on the ALDL connector to determine if any of the connections are broken or shorting out against the chassis. The serial data circuit typically goes short because of a failed controller or module (CCM, ECM and ABS/ASR). It's just one tan wire connected to all the modules, when it's shorted or a module fails it pulls the whole bus down and nothing is able to communicate throwing the code.

Disconnect the aftermarket stereo, third party amps and any other non factory electronics during testing. Unplug any factory modules with the exception of the CCM and ECM which might restore the serial connection and remove the C41. If none of this works after checking all the wires for proper connections and you still have the Code C41 error then suspect the Ignition Control Module (ICM) and test that. If that passes I would then finally suspect the ECM (PCM) for replacement.

 

Hi guys,

I have the same issue here C41 code, in my case the car is drivable, but i have misfires at low rpms and the gasoline is not being burn properly, so i keep getting liquid fuel at my exhaust.
I already send my ECM for repair, and the ECM specialiist made service and diagnose as it is EVERYTHING OK, Never the less i still have the C41 code.

I dont know if even with an OK diagnose the ECM might be Faulty

Thanks for your support.

 

That C41 code sounds non-related to your enrichment running issue.

Did you check for spark in all cylinders? That's the first thing I would do followed by troubleshooting for a stuck injector.

As for the C41 I assume you have a 91 based on your member description. Wouldn't trust any supposed ECM specialist claiming everything is OK simply from a bench inspection for a 35 year old computer. It's far easier to find a cheap replacement ECM from many cross referenced part compatible cars on Ebay or car-part.com and swap over your EPROM and test it in the car yourself to see if the C41 code goes away to rule out if it's the ECM once and for all. Then if the code still doesn't go away then you know it's something more complex like the dreaded airbag derm modules that are known to be problematic in the 91's or the serial connection wires.

 

Thanks mate, the car is now at the workshop, all injectors were ultradirty and were not able to pulverize the fuel as it should, they already cleaned them and they told me now they are working "ok".
At least this give me chance to import some bosch injectors, they haven installed them yet to see if the problem was solved by this, hopefully it will.

As for the ECM i already order one, hopefully it will solve the c41 code. But my biggest concern was to be related to the enricment issue, so if with the injectors issue corrected also corrects my enrichment issue, this buys me time for the ECM to arrive and to do some electrical work on it.

Thanks very much for your reply.