P1875

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Four Wheel Drive (4WD) low circuit consists of the Vehicle Control Module (VCM), a transfer case switch, and the circuit wiring. The transfer case switch controls the 4WD low signal on circuit 1694. When the operator selects 4WD low, the transfer case switch closes and the 4WD low signal voltage on circuit 1694 changes from ignition voltage to zero volts. The VCM then compensates for transfer case gear reduction in the transmission Output Shaft Speed (OSS) signal. The VCM uses the transmission OSS signal to adjust shift points, line pressure and Torque Converter Clutch (TCC) scheduling.

When the VCM detects a continuous open or short to ground in the 4WD low circuit, then DTC P1875 sets. DTC P1875 is a type B DTC.

CONDITIONS FOR SETTING THE DTC

DTC P1875 sets if the following conditions are met two consecutive times:

^ No Throttle Position (TP) Sensor DTCs P0122, or P0123

^ No Vehicle Speed Sensor Assembly (VSS Assy.) DTCs P0502 or P0503

^ No TCC Sol. Valve DTC P0740

^ No TCC Stuck ON DTC P0742

^ No 1-2 SS Valve DTC P0751 or P0753

^ No 2-3 SS Valve DTC P0756 or P0758

^ No Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) DTC P1810

^ No TCC Pulse Width Modulation (PWM) Sol. Valve DTC P1860

^ The engine speed is greater than 450 RPM for 5 seconds.

^ Not in fuel cutoff.

^ The gear range is D4.

^ The vehicle speed is greater than 11 km/h (7 mph).

^ The TP angle is 17-50%.

^ The engine torque is between 50-400 ft. lbs.

^ The engine vacuum is between 0-105 kPa.

^ The shift solenoid performance counters are zero.

^ The Transmission Fluid Temperature (TFT) is 20-130°C (68-266°F).

^ All of the above conditions are met and either of the following fail conditions occurs two consecutive times:

- Four-wheel drive low is stuck ON for 5 seconds. The TCC slip speed is -3000 to -50 RPM. Four-wheel drive low range is not engaged. The speed ratio is 0.8-1.2. (The speed ratio is the engine speed divided by the transfer case output speed).

- Four-wheel drive low is stuck OFF for 10 seconds. The TCC is commanded ON. The TCC slip speed is 100-3000 RPM. Four-wheel drive low range is engaged. The speed ratio is 2.5-2.9.

ACTION TAKEN WHEN THE DTC SETS

^ The VCM illuminates the Malfunction Indicator Lamp (MIL).

^ The VCM commands a normal shift pattern (not a 4WD low shift pattern).

^ DTC P1875 stores in VCM history.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns OFF the MIL after three consecutive trips without a failure reported.

^ A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.

^ The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS

^ Inspect the wiring at the VCM, the transfer case switch connector and all other circuit connecting points 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

^ Moisture intrusion

^ Corrosion

^ When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

TEST DESCRIPTION

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

3. This step tests for a short to ground in circuit 1694.

4. This step tests for an open in circuit 1694 or a faulty transfer case switch.