Main code 64 indicates the ECU has detected a voltage signal from the retarder request modulation sensor (consisting of a module and a retarder control device) in either the high or low error zone. These codes can be caused by faulty wiring, faulty connections to the resistance module or retarder control device, a faulty resistance module, a faulty retarder control device, or a faulty ECU. Power wire 133 and ground wire 135 for the retarder modulation request sensor share a common power and ground with the TPS and OLS devices. A short-to-ground on the common power wire causes a ?sensor failed low? code for the other devices (Codes 21 12, and 14 12). An open or a short-to-ground on retarder modulation request sensor signal wire 164 results in a Code 64 12 only.
Allison WTEC II Fault Code: 64 PID: SPN: 12 FMI: Retarder modulation request sensor, failed low
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