Loss Of Accelerator Input

[Signature620]

Hi everybody. I've been involved with a job lately on a CM871 CPL3774 (Aus with EGR and DPF) & I'm looking for some ideas on where to go next.

You drive along and all of a sudden you lose accelerator. Once you let off the accelerator pedal it's fine to use again.
Monitoring with Insite, when it happens, eng operating state doesn't change, both accelerator signal and supply voltages dont change, but pedal position changes to 0%. There are no fault codes, and nothing accelerator or battery voltage related is blocked on the calibration.

We've tried a different calibration as it was deleted by someone else, a test ECM, replacing the TPS, rewiring the accelerator and rewiring the VSS. The symptoms haven't changed.

When monitoring 'accelerator pos before filters' (or something along those lines), with CTerm, the reading stays at the actual physical position, but the 'commanded accelerator position' shows 0%.


It's not something I've come across before. Usually these ECMs are very quick to log faults for accelerator or VSS issues. Something is triggering the ECM to cut the accelerator but it's strange that it resets when you let off.

[Chamberpains]

What is the make and model of the truck?

Have you done the simple "ECM smack" to see if it hiccups or goes haywire?

Which TPS wires did you replace? The twisted ones around the back of the engine were the culprit in my similar cm870 problem. I replaced all 3 twisted wires as a resolution.

[Signature620]

It's a KW K200. The whole TPS circuit was rewired including the common supply. We've tried a good spare ECM.

[Rawze]

tarnished pins in the cab connector that mates to the firewall?

could be the primary signal is fine, but the secondary signal is cutting out?

could also be something commanding it to 0 on the J1939?

could also flash it with factory non-deleted file to see if problem goes away, or if it throws a fault?.

[tariqzai]

I had this problem with two of my volvos, one (with CM 2250) turned out to be the wiring manifold in the firewall, greased and torque it and never did that again. The other volvo has CM871 and I could not figure out the problem yet. It does it sometimes frequently and sometimes it's ok for days.

[Rawze]

It is also likely possible to dig deeper using CT and monitoring the logic choice/flow control to see why it is choosing 0% when the inputs are still at normal state. Even so, It might not tell you much about where the problem lies, since it has been confirmed to be external to the ecm (you swapped ecm's).

The Top tier of that selection pathway ...
maybe monitor the 'Combustion_Control_Path_Owner' ram parameter and see what values it is switching into and out of when it acts up.

[Signature620]

Thanks Rawze, I'll have a better dig in CT next time I see the truck.

It's a COE and the accelerator has been rewired from the pedal to the ECM with no bulkheads/connectors/etc in between.

I have monitored the ABS with Bendix software as the fault occurs to see if it's related but all wheel speeds are in range and there's no ABS faults.

This truck doesn't have anything else on the datalink. It's a manual, doesn't have stability cntrl and doesn't have a body module. The only thing that would've been multiplexed was the regen switch but that's out of the picture now.

[redbeard]

By chance is it an auto shift? Had one that did same thing and replaced harness and sensors on trans as it would lose contact to what gear it was in.