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Accelerator Pedal Wiring/switch

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Well, I thought I had cracked the engine brake issue I reported on with the replacement of a relay. That turned out to be a fluke it was not the fix the engine brake failed after 38 miles.

I had a dual fix, sort of, when I replaced the relay; I had also been grubbing around under the dash and had seen that the harness to the accelerator pedal was taut at full forward pedal slide extension. (Towards the driver) I tried to correct that and also checked the plug and wires for any problems.

So the coach went in for its annual service and the engine brake was fine. The mechanic took her to the local government test station (over here in the UK after a vehicle is 3 years old it has an annual test) and did 20 miles each way without an issue on the engine brake.

I collected her and was nearly home and the engine brake stopped working!!!!!! I drove straight back to the garage.

They looked at the accelerator connections and declared them OK. Various other checks revealed a Cummins service bulletin on Engine Brake wiring in the rocker box. A replacement harness and special clips were available for a solution to possible chaffing causing an intermittent fault. Well we all thought that was it.

I picked her up yesterday and once again was nearly home, and sitting at some lights, thought that the pedal slide was too close so moved it to suit me. Turned down the hill and the engine brake was not working!!! I stopped and fiddled with the plug and wires to the accelerator. The engine brake returned!! So it must be in this plug/wiring or switch.

What I find difficult is that I have no issues with the throttle itself so which of the 6 wires has an effect on the engine brake?

Anyone have any thoughts or help here?


2008 CC Allure Cummins ISL 425

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Michael, this is what I have on file, some items may vary; but it should be close.

Accelerator peddle section of the circuit has 3 of the 6 wires. Throttle control to ECM.

Position connections accelerator portion voltage control, feeding main engine harness.

A= Green and Blue wire---Return=ground

B= Red and white wires---peddle position voltage=accelerator voltage to engine harness

C= Black and red wire---Supply voltage to peddle from engine harness

The other 3 wires are from the Idle position switch part of the assembly, Idle Validation switch feed to ECM.

Listed as A,B and C

A= Red orange---normally open side of the switch. When accelerator is depressed, pin A connects to pin C the common return wire to the engine harness main connector.

B= Blue normally closed side of switch.. Accelerator not depressed.

C= Black and white wire switch common.

Let me know if this helps. I do have more information if you like, but things very some from model to model.


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For those who responded to my various posts on this section and others I am pleased to report a finite solution.... I hope says he tempting fate!

After replacing, Hi off Lo switch, relay, removing brakeswitch.com box, replacing some battery connections, harness inside rocker box for brake control, I finally homed in on the throttles sensor at the accelerator pedal.

Lucky breaks pointed me at it or the harness. After much thought and feedback from the sensor manufacturer I replaced the sensor and had a harness on standby.

A 40 mile test proved positive but I still really wanted a 100 mile plus trip without issue. BUT, I built a good rapport with the UK distributor of these sensors and he agreed to put the old unit to a severe test.

Well he telephoned this morning, the sensor was shot! The idle switch was failing or failed and there were other symptoms developing like a flat spot in the acceleration curve.

So it was about to totally die! I feel more confident with my opening gambit...



2008 Allure 31683 ISL 425

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