Allison Automatic Transmission

DTC P1860

Circuit Description

The torque converter clutch (TCC) solenoid, F solenoid, is a pulse width modulated (PWM) solenoid. Pulse width modulation occurs when the signal from the transmission control module (TCM), to a solenoid, is modulated at an established frequency, causing the steel check ball in the solenoid to rapidly open and close the solenoid passage. This serves to vary the output fluid pressure.

DTC P1860 is a type B DTC.

Conditions for Running the DTC

- The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
- Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
- The TCC is commanded ON.

Conditions for Setting the DTC

DTC P1860 sets when the TCM detects an open circuit, a short to power, or a short to ground in the F solenoid circuit for 1.5 seconds.

Action Taken When the DTC Sets

- The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
- DTC P1860 will be stored in TCM history.
- The TCM inhibits TCC engagement.
- The TCM freezes shift adapts.
- Reverse operation is disabled.

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids

- 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 or 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 condition.
- Solenoids are sensitive to battery voltage spikes and poor ground connections.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. This step tests the system voltage.
3. This step tests the command from the TCM to F solenoid.
4. This step tests the wiring harness for opens/shorts.
5. This step tests the internal wiring harness.
6. This step tests the resistance at F solenoid.