Allison 3000 & 4000 Gen 5 C1312 Fault Code Solution

Here is the illustration show you guide on how to repair and solve Allison 3000 & 4000 Gen5 fault code C1312 retarder request sensor circuit low.

Allison 3000 & 4000 Gen 5


Inhibits retarder operation if not using J1939 datalink


For more Diesel machine repair,please refer to:

2023 Diesel DTC Solutions V2.9.98+ Diesel Explorer 2.0+Instruction



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. If used, the input is monitored by software, which then controls a retarder pressure solenoid.


NOTE: J1939 Retarder Select, Non-Engine (RSNE) and/or TSC1 messages may be used in addition to or instead of an RMR sensor to request the amount of retardation desired.


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 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 request.



When DTC C1312 is active, the following conditions occur:

1 The TCM does not iluminate the CHECK TRANS light.

2 DTC is stored in TCM history.

3 The retarder will no longer apply based on input from the RMR sensor.



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.



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 filed 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 Analog retarder request input (i.e. RMR inputs) enabled during TCM programming without RMR module.

3 Non-retarder application has autodetected retarder or had the CMC Override Retarder Autodetect set to ‘Present’.

4 Missing RMR module.

5 Defective sensor sharing 5V supply.

6 5V wire open or grounded in transmission internal harness.

7 Broken or defective connector assemblies allowing pushed back pins to short together.

8 Unlocked cnnectors mssig seal plugs alwin moisture in conetr.

Review applicable information within CONTROL SYSTEM AND TRANSMISSION SPECIFICATIONS to find additional circuit specifications, system and connector diagrams, and troubleshooting tips.

More Allison repair case,please refer to Allison Trouble Repair

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