DTC P1875 4WD Low Switch Circuit Electrical 4.3L Only
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 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 TP Sensor DTCs P0122, or P0123. |
| • | No 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 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 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 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.
-
This step tests for voltage to the TCCM when you select 4LO on the transfer case selector switch.
-
This step tests for ignition voltage to the transfer case selector switch.
-
This step tests if the TCCM is faulty.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 |
Important: Before clearing the DTC(s), use the scan tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the VCM. Does 4WD Low on the scan tool read Disabled when you select 4HI, and then Enabled when you select 4LO? | -- | Go to Diagnostic Aids | |||||
Does the test lamp illuminate when you select 4LO and turn OFF when you select 4HI? | -- | |||||||
4 |
Does the test lamp illuminate when you select 4LO and turn OFF when you select 4HI? | -- | ||||||
Install the test lamp to ground and probe terminal C at the transfer case selector switch. Is the test lamp ON? | -- | |||||||
6 |
Refer to General Electrical Diagnosis Procedures. Did you find and correct an open or short to ground condition? | -- | -- | |||||
7 | Replace the transfer case selector switch. Refer to Selector Switch Replacement. Is the replacement complete? | -- | -- | |||||
8 |
Refer to General Electrical Diagnosis Procedures. Did you find and correct an open or short to ground condition? | -- | -- | |||||
Install a fused jumper wire from terminal C1 to terminal C3 of the TCCM harness connector. Does 4WD Low read Enabled on the Scan Tool ? | -- | |||||||
10 | Replace the TCCM. Refer to Transfer Case Control Module Replacement. Is the replacement complete? | -- | -- | |||||
11 |
Is the test lamp ON? | -- | ||||||
12 | Inspect circuit 1694 (GRY/BLK) for an open or short to ground. Refer to General Electrical Diagnosis Procedures. Did you find and correct an open or short to ground condition? | -- | -- | |||||
13 | Replace the VCM. Refer to VCM Replacement/Programming . Is the replacement complete? | -- | -- | |||||
14 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
