P1875

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The 4 Wheel Drive (4WD) Low circuit consists of the Powertrain Control Module (PCM), transfer case switch and the circuit wiring. The transfer case switch is used to control the 4WD Low signal on circuit 1694. When the operator moves the 4WD selector lever to 4WD Low, the transfer case switch closes, and the 4WD Low signal voltage on 1694 changes from B+ voltage to zero volts. The PCM then compensates for transfer case gear reduction in the transmission Output Shaft Speed (OSS) Sensor readings. The PCM uses the transmission OSS Sensor signal in order to adjust shift points, line pressure and Torque Converter Clutch (TCC) scheduling.

If the PCM detects a continuous open or short to ground in the 4WD Low signal circuit , then DTC P1875 sets. DTC P1875 is a type B DTC.

CONDITIONS FOR SETTING THE DTC

^ No Input Shaft Speed (ISS) Sensor DTCs P0716 or P0717.

^ No OSS Sensor DTCs P0722 or P0723.

^ No TCC Pulse Width Modulation (PWM) Sol. Valve DTC P0742.

^ No 1-2 SS Valve DTCs P0753 or P0751.

^ No 2-3 SS Valve DTCs P0758 or P0756.

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

^ No TCC PWM Sol. Valve DTC P1860.

^ The gear range is D4.

^ The Accelerator Pedal Position (APP) Angle is 9-99%.

^ The engine is running greater than 475 RPM for more than 7 seconds.

^ The Transmission Fluid Temperature (TFT) is 20°-130°C (68°-248°F).

^ All of the above conditions are met and one of the following fail conditions exist:

- Four wheel drive low circuit is closed (grounded) for greater than 5 seconds in any one gear, and the transfer case ratio is 0.95-1.05:1 for 2 occurrences.

- Four wheel drive low circuit is open for 1.5 seconds in two different commanded gears, and the transfer case ratio is 2.65-2.75:1 for the first occurrence.

ACTION TAKEN WHEN THE DTC SETS

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

^ The PCM freezes shift adapts from being updated.

^ When stuck ON (closed), the PCM assumes a non 4WD low state for a transmission shift pattern.

^ When stuck OFF (open), the PCM assumes a 4WD low state for a transmission shift pattern.

^ DTC P1875 is stored in PCM history.

CONDITIONS FOR CLEARING THE MIL/DTC

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

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

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

DIAGNOSTIC AIDS

^ Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the transmission transfer case connector. Look for the following problems:

- 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, massage the wiring harness while watching the test equipment for a change.

^ A faulty FRT axle actuator may cause a delayed or a No upshift condition in 4WD LOW.

TEST DESCRIPTION

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

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

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