P0703

ALLISON AUTOMATIC TRANSMISSION

DTC P0703

DTC P0703 Step 1 - 7:

DTC P0703 Step 8 - 11:

Circuit Description for Allison Automatic Transmission
A mechanical switch attached to the brake pedal sends a signal to the Transmission Control Module (TCM) indicating the service brake has been applied. This signal is either ignition voltage or a ground signal depending on the calibration installed in the TCM.

Conditions for Running the DTC
The components are powered and ignition voltage is greater than 9 V and less than 18 V for a 12 V TCM.

Conditions for Setting the DTC
The TCM sets a DTC when either of the following conditions is detected.
^ The vehicle accelerates 10 or more times with the brake switch in the ON position.
^ The vehicle decelerates 10 or more times with the brake switch in the OFF position.

Action Taken When the DTC Sets
^ Use default assumption that brake is OFF.
^ TCM inhibits TCC engagement.

Conditions for Clearing the MIL/DTC
A scan tool may be used to clear the code 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
DTC P0703 indicates that the TCM did not see the proper input signal for service brake status during an acceleration or deceleration cycle. This may indicate an open or short in the TCC Brake Switch/Cruise Control Release Circuit or a faulty Stop Lamp Switch.
^ Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
- A bent terminal
- A backed-out terminal
- A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation
^ When diagnosing for an intermittent short, open massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a fault.

Test Description
The number(s) refer to the step number(s) on the diagnostic table.
2. This step tests brake switch status.
3. This step tests for voltage at the C1 conned- for.
4. This step tests for voltage after the stop lamp switch.
5. This step tests for voltage before the stop lamp switch.