Allison 3000 & 4000 Gen 4 Fault Code: P071A RELS Input Failed On

DIAGNOSTIC RESPONSE:
Inhibit RELS operation

CIRCUIT DESCRIPTION:
When Function AS: Reduced Engine Load at a Stop (RELS) is active, the Transmission Control Module (TCM) automatically commands transmission operation at a reduced load state similar to Neutral (N). The purpose of the function is to reduce the load on the engine when the vehicle is stopped which improves fuel economy and reduces heat load of the transmission in high start/stop duty cycles. To active RELS, the vehicle must be in first range, at a stop, service brakes applied, accelerator pedal approximately at 0%, and the TCM GPI terminal for RELS must see V+, V Ign, or V Bat. RELS deactivates when the service brake is released. Supplemental controls such as a door switch or a RELS enable dash switch may be wired in series with the service brake pressure switch or, alternately, a vehicle Programmable Logic Controller (PLC) output may switch the RELS signal as a result of a service brake pressure switch input to the PLC. The signal used to activate RELS may be on W102, W123, or W143, depending upon which Input/Output (I/O) package was selected in the TCM calibration. RELS typically uses a switch-to-battery input (analog). Refer to the OEM Technician’s Library for RELS wiring information. RELS is not available for all applications and cannot be used with a 2nd gear start. The service brake status message available on CAN1/CAN2 datalink, e.g., SAE J1939, is not a valid input for the RELS feature.

Reduced Engine Load at Stop (RELS):
GPI#: 1
GPI Type: +
TCM Pin Number: 23
Wire Number: 123
Wire Color: Green
Termination Points: Service Brake Pressure Switch to V+ or PLC Output

GPI#: 2
GPI Type: +
TCM Pin Number: 2
Wire Number: 102
Wire Color: Yellow
Termination Points: Service Brake Pressure Switch to V+ or PLC Output

GPI#: 3
GPI Type: +
TCM Pin Number: 43
Wire Number: 143
Wire Color: Blue
Termination Points: Service Brake Pressure Switch to V+ or PLC Output

CONDITIONS FOR RUNNING THE DTC:
1. TCM is calibrated to receive the RELS input signal.
2. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test will run at 1 second intervals.

CONDITIONS FOR SETTING THE DTC:
RELS ON for 3 acceleration events without seeing RELS change state.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P071A is active, the following conditions occur:
1. The DTC is stored in the TCM history.
2. The TCM does not illuminate the CHECK TRANS light.
3. TCM inhibits RELS operation.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
The diagnostic tool may be used 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 the DTC recurring.

DIAGNOSTIC AIDS:
This DTC may be caused by:
1. Short to power or short to another wire for the GPI circuit controlling RELS feature, i.e., W102, W123, or W143.
2. For service brake integrations, defective switch or incorrect wiring, e.g., pressure switches are closed when they should be open. If RELS enable switch or door switch integrated in series, all switches would need to be stuck closed or wired on wrong side of switches, e.g., normally closed side vs normally open side.
3. For PLC RELS integrations, a miswired, misprogrammed, or defective circuit from PLC controlling the TCM GPI signal for RELS that is maintaining circuit above 3.4 volts with service brakes released.
4. RELS enabled in TCM programming in error.
5. TCM ground is at different voltage potential than the ground of the OEM voltage source responsible for switching GPI circuit controlling RELS, e.g. PLC, vehicle ignition, body controller, etc.
6. Defective TCM.