[2001 S80 2.9] VIDA name for signal that turns on ECM relay?

[DanSC]

Short question: I am seeking information on what logic and event chain sends the signal to the electronic throttle module (ETM) relay to send battery voltage to the electronic throttle module.

Longer explanation

I recently took a trip, and my 2001 S80 2.9 sat for ten days. When I returned, it did not start as promptly as usual, though I did not think anything of it. It was quite hot, and I thought the car needed to cool down. A few days later, it sometimes does not start, though it will start if I crank the car a second time. A few days after that, it will not start, and it shows me the message "IMMOBILIZER: CHECK MANUAL."

As other posts on this forum describe, the manual doesn't really mention immobilizer errors. I tried different keys, the lock-unlock, and repeated turning off the ignition switch. Occasionally, the car would start, though it usually would not. I connected my VIDA unit to the car, and verified that all immobilizer checks at least reported to VIDA as passed.

Eventually, the car throws several errors along with the immobilizer message: ABS, SRS, etc. Investigating this suggested a low battery, and sure enough, it was out of warranty and would not charge to 12 V. I replaced the battery, and the car quickly started...once.

The car then produced two different VIDA codes:

• ECM-8010, faulty battery signal, maybe from me occasionally disconnecting the battery?
• CEM-902A and/or CEM-1A5D, a combination of missing ETM or faulty ETM signal

After hunting for and not finding bad fuses or relays, I found this excellent ETM troubleshooting guide from XeMODeX (PDF). I followed the steps and found that I did not have battery voltage between pins 5 and 6 on the ETM engine plug despite the good fuse; It was only 1.3 V. I switched the relay with a different one on the board, which still didn't fix the issue. I then re-seated the large harness plug that entered the top of the engine fuse panel. The fuse received battery voltage, and the car started.

As I cleaned up my tools, I would go back and check the voltage, which would sometimes drop down to 1.3 volts. The terminal that connects the relay to the fuse was also at 1.3 volts.

My questions now are:

• What specifically tells the CEM to send a signal to turn on the ETM relay, and is it something I can see in VIDA?
• If a relay is OFF, or removed, why would the circuit downstream of the battery voltage still have a 1.3 V potential between it and ground, other than a weak ground connection?

[DanSC]

I now know there is an ETM forum, so I have posted this issue there.

[DanSC]

After some more digging, the ETM seems to be perfectly fine. My current diagnosis centers on the Engine Control Module Main Relay (what I had previously called the ETM relay). The relay sends power to the ETM and coils, so it needs to click on before the engine to start. The car starts if I bypass the relay with a relay circuit test tool.

Between swapping relays and testing voltages at the proper wiring terminals, I have not found a pattern for whether the ECM will send a signal to turn on the relay. Using the wiring diagram for the car, I know which wire and pin from the ECM tells the relay to close: the Yellow-White Wire traveling from ECM pin B:38 through connector pin 15/24:6. I have added selections from the wiring diagram at the bottom of this post. I know both wires A and B in the green boxes don't go to the ECM relay; I just drew the green boxes too large.

I know how to test the continuity of the wire. I don't know what Volvo calls the signal leaving the B:38 pin, if I can find the naming guide between ECM pins and functions in VIDA or elsewhere, or if VIDA will even show me if the ECM is commanding the relay to activate to close, I can determine if the error is in the wiring between the ECM and the relay. I assume the computer commands the control circuit in the relay to ground; please let me know if that is wrong. I hope to see that data point in VIDA before tearing apart what may be a perfectly good wiring harness.

Any help would be greatly appreciated.

2001 Volvo S80 Wiring Diagram Page 32 section

2001 S80 wiring diagram page 32.png (242.56 KiB) Viewed 3443 times

2001 Volvo S80 Wiring Diagram Page 33 section

2001 S80 wiring diagram page 33.png (180.3 KiB) Viewed 3443 times

[DanSC]

I learned a few things over the weekend

• I suspect the CEM-ECM communication datapoint is the CEM communication menu is the closest thing to an indicator that the ECM is sending signals to relays
• While I didn't find a way to activate the engine management relay in the Activations menu, I can turn on the fuel injectors, and they draw power through the engine management relay.

I also learned something specific to my case. While working under my hood, I bumped the box that holds the ECM and Transmission Control Module (TCM), and the throttle module clicked on for a moment. While I haven't been able to repeat that exact bump, I suspect a short exists in that area. I'll know more once a module removal tool arrives tomorrow.

[DanSC]

I forgot to update this...my apologies.

I think the fault was a worn plastic bracket that holds the ECM & TCM in the plastic module box and connected to the wire harness. Replacing that solved all my issues. Before I replaced the bracket, the only way to reliably make the car run was to use a manual-switched relay in place of the ECM relay, suggesting an intermittent fault in the connection in the circuit that turns on that relay.

As for finding a new bracket (part 9456590)...good luck! I don't think Volvo manufactured them, and I had to hope a used part would work. Maybe someone can guilt Volvo into releasing a CAD file so we can make our own.

[abscate]

That b38 pin will be pulled to ground by the ECM to power up that relay and send 12v down to the fusebox 11/B5

Without knowing the ECM operating code you cannot go further than that to troubleshoot the B38 pin function, and thst knowledge is Volvo proprietary