Allison 4000 RDS - Fault Code 1305 Retarder Oil Temp High Signal

Question

My 2018 Kenworth dump truck is throwing a trans light and code 1305 after getting up to operating temp. The gauge on the dash looks normal, but the scanner shows the retarder oil temp is pinned at 300 degrees even when the pan temp is only 180. The retarder has been acting erratic and won't engage properly when I'm loaded.

Carlos Diaz · Accepted Answer

The issue ended up being a failed internal thermistor on the retarder body. I had to drop the retarder control valve module and replace the internal wiring harness (Part #29543162) which includes the temperature sensor. After installing the new harness and a new gasket, I cleared the codes with Allison DOC and the retarder is now modulating correctly with temperatures matching the dash gauge. Total cost for parts was about $320 plus 4 hours of labor.

hd_trucker_77 · Answer

Code 1305 usually points to an open circuit on the retarder temperature sensor circuit. You should check the internal wiring harness, as the heat cycles inside the retarder housing can cause the insulation to become brittle and crack near the thermistor.

turbo_tony · Answer

If you find that the sensor is okay, inspect the bulkhead connector on the side of the transmission. Moisture gets trapped in the weather pack and can corrode the pins for the retarder circuit specifically, leading to high resistance codes.

Pete Sanders · Answer

Before replacing parts, perform a resistance check at the 80-pin TCM connector. You want to see between 300 to 3000 ohms depending on the temperature; if it reads infinite, you definitely have a break in the wire or a dead sensor.

Allison 4000 RDS - Fault Code 1305 Retarder Oil Temp High Signal

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