P1875

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The 4WD low circuit consists of a transfer case selector switch, a Transfer Case Control Module (TCCM), circuit wiring and the Vehicle Control Module (VCM). When the operator selects 4WD LOW, the TCCM receives a momentary signal from the selector switch. If all conditions for 4WD low are met, the TCCM allows the electric motor in the transfer case to make the shift. When 4WD low is engaged, voltage on circuit 1694 to the VCM changes from B+ to zero. The VCM uses the 4WD low switch signal to adjust the transmission output speed signal to the VCM. This compensates for transfer case gear reduction. The VCM uses the transmission output speed 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 (VSS) Assy. DTCs P05O2 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 TFP Val. Position Sw. DTC P1810.

^ No TCC 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 Throttle Position (TP) angle is 17-50%.

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

^ 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 selector switch connector, the TCCM 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 voltage to the TCCM when you select 4LO on the transfer case selector switch.

5. This step tests for ignition voltage to the transfer case selector switch.

9. This step tests if the TCCM is faulty.