2008 Western Star 4900 - Loss of Throttle Response (Dead Pedal)

Question

I'm driving an 08 Star with the Series 60. Lately, I'll be cruising down the road and suddenly the engine just drops to idle. I can floor the pedal and nothing happens. If I pump the pedal a few times or restart the truck, it starts working again.

It's extremely dangerous when pulling into traffic. There's no check engine light initially, but sometimes the 'Check Engine' flash code 21 shows up. I suspect the pedal assembly, but I've heard it could be a wiring rub through the firewall.

VolvoVince · Accepted Answer

✅ Confirmed fix: The Series 60 uses a triple-redundant TPS (Throttle Position Sensor). If the idle validation switch and the throttle sweep don't agree, the ECM ignores the throttle for safety. Replacing the entire Williams throttle pedal assembly fixed it. The internal potentiometers get dead spots over time from being held in the same cruising position.

DefDeleteDan_NO · Answer

Check the battery power to the ECM. If the ECM loses its main 12V feed for even a millisecond due to a loose fuse or wire, it can reset the throttle calibration until the key is cycled.

2008 Western Star 4900 - Loss of Throttle Response (Dead Pedal)

Suggest a repair