Allison 3000 & 4000 Gen 4 Fault Code: C1312 Retarder Request Sensor Failed Low

DIAGNOSTIC RESPONSE:
Inhibits retarder operation if not using J1939 datalink

CIRCUIT DESCRIPTION:
The TCM may be calibrated to receive a Retarder Modulation Request (RMR) signal from a retarder request sensor, sometimes called a resistance module or RMR device.

NOTE: A TCM calibration with the retarder feature can be specified to:
1. Only receive an analog RMR on W156.
2. Only receive the RMR message on SAE J1939.
3. Receive both an analog RMR signal and a SAE J1939 RMR message.

The TCM is connected to the retarder request sensor by:
1. A 5V reference voltage (W112),
2. Retarder request signal (W156), and
3. Analog ground (W158).

The TCM provides a 5V reference voltage to the retarder request sensor. A voltage driver network in the sensor produces a retarder request signal in response to inputs from the retarder control device(s). The TCM interprets this signal as a percent retarder requested.

CONDITIONS FOR RUNNING THE DTC:
1. Retarder and analog RMR source must be enabled in calibration.
2. Retarder must be autodetected or CMC Override Retarder Autodetect must be programmed to ‘Present’.
3. After TCM initializes normally and engine speed is above 200 rpm, this DTC test will run at 0.25 second intervals.
4. DTC not active.

CONDITIONS FOR SETTING THE DTC:
DTC C1312 sets if the TCM is calibrated to receive the retarder request signal, and the signal voltage is less than 0.3V for five seconds.

ACTION TAKEN WHEN THE DTC SETS:
When DTC C1312 is active, the following conditions occur:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in TCM history.
3. TCM will inhibit retarder operation if not using datalink for RMR message.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
DTC C1312 indicates the TCM has detected a voltage signal from the retarder request sensor in the low error zone and may be caused by the following:
1. Open or short to ground in W112 or W156 circuits.

NOTE: Shorts or opens in W112 typically will log other sensor failed low DTCs that are using W112 (5V), such as the Oil Level Sensor (OLS), Electronic Brake System (EBS) pressure sensor, or analog Throttle Position Sensor (TPS). Shorts or opens in W156 (RMR analog signal) only causes DTC C1312.

2. Non-retarder application has autodetected retarder or had the CMC Override Retarder Autodetect set to ‘Present’.
3. Missing RMR module.
4. Defective sensor sharing 5V supply.
5. 5V wire open or grounded in transmission internal harness.
6. Broken or defective connector assemblies allowing pushed back pins to short together.
7. Unlocked connectors, missing seal plugs allowing moisture in connectors.
8. TCM issue.

Review applicable information in Control System and Transmission Specifications to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.