DTC P1875 4WD Low Switch Circuit Electrical Gas
Circuit Description
The 4WD low circuit consists of the Vehicle Control Module (VCM), 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 circuit 1694 changes from B+ voltage to zero volts. The VCM then compensates for transfer case gear reduction in the transmission Output Shaft Speed (OSS) Sensor readings. The VCM uses the transmission OSS Sensor signal in order to adjust shift points, line pressure and Torque Converter Clutch (TCC) scheduling.
If the VCM detects a continuous open or short to ground in the 4WD Low signal circuit, then DTC P1875 sets. DTC P1875 is a type D DTC. For California emissions vehicles DTC P1875 is a type B DTC.
Conditions for Setting the DTC
| • | No MAP DTCs P0106, P0107 or P0108. |
| • | No TP Sensor DTCs P0121, P0122 or P0123. |
| • | No OSS DTCs P0502 or P0503. |
| • | No A/T ISS DTCs P0716 or P0717. |
| • | No 1-2 SS Valve DTCs P0751 or P0753. |
| • | No 2-3 SS Valve DTCs P0756 or P0758. |
| • | No TFP Val. Position Sw. DTC P1810. |
| • | No TCC PWM Sol. DTC P1860. |
| • | The engine is running at least 475 RPM for 7 seconds. |
| • | The TFP Val. Position Sw. is D4. |
| • | The TP Sensor is 10-100%. |
| • | The TFT is 20-125°C (68-248°F). |
| • | Engine torque is 67 N·m (50 lb ft): |
| - | 540 N·m (400 lb ft) 5.7L |
| - | 675 N·m (500 lb ft) 7.4L |
| • | Vehicle speed is greater than 1.5 mph. |
| • | All of the above conditions are met and one of the following conditions occur: |
| - | Four wheel drive low circuit is closed (grounded) for more than 1.5 seconds with a transfer case ratio of 0.95-1.05:1, for 5 occurrences. |
| - | The four wheel drive low circuit is open for 1 second with a transfer case ratio of 2.68-2.76:1 in any two gears for 4 occurrences. |
Action Taken When the DTC Sets
| • | The VCM illuminates the Malfunction Indicator Lamp (MIL), for California emissions vehicles. |
| • | The VCM assumes a 4WD Low state for transmission shift patterns when stuck OFF. |
| • | The VCM assumes a non 4WD Low state for transmission shift patterns, when stuck ON. |
| • | The VCM freezes shift adapts from being updated. |
| • | DTC 1875 is stored in VCM History. |
Conditions for Clearing the DTC
| • | For California emissions vehicles, 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 for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections at the transmission 20-way 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. |
| • | First diagnose and clear any engine DTCs or TP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset. |
| • | Low pump pressure and a slipping trans can cause DTC P1875 to set. |
| • | Transfer case gear ratio is calculated by dividing the A/T ISS by the OSS. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for a short to ground in circuit 1694.
-
This step tests for an open in circuit 1694 or a faulty transfer case switch.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check (5.7L) or Powertrain On Board Diagnostic (OBD) System Check (7.4L) | |||||
2 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the stored Freeze Frame and Failure Records from the VCM. Does the 4WD Low on the scan tool display Disabled when 4WD HI is selected, then Enabled when 4WD Low is selected? | -- | Go to Diagnostic Aids | |||||
Does the 4WD Low on the scan tool indicate Enabled? | -- | |||||||
Does 4WD Low on the Scan Tool indicate Enabled when circuit 1694 is grounded? | -- | |||||||
5 | Replace the transfer case switch. Refer to Transfer Case Switch Replacement. Is the replacement complete? | -- | -- | |||||
6 |
Refer to General Electrical Diagnosis in Wiring Systems. Did you find the condition? | -- | ||||||
7 |
Refer to General Electrical Diagnosis in Wiring Systems. Did you find the condition? | -- | ||||||
8 | Replace the VCM. Refer to VCM Replacement/Programming (5.7L) or VCM Replacement/Programming (7.4L). Is the replacement complete? | -- | -- | |||||
9 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
DTC P1875 4WD Low Switch Circuit Electrical Diesel
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 ISS Sensor DTCs P0716 or P0717. |
| • | No OSS Sensor DTCs P0722 or P0723. |
| • | No TCC PWM Sol. Valve DTC P0742. |
| • | No 1-2 SS Valve DTCs P0753 or P0751. |
| • | No 2-3 SS Valve DTCs P0758 or P0756. |
| • | No TFP Val. Position Sw. DTC P1810. |
| • | No TCC PWM Sol. Valve DTC P1860. |
| • | The gear range is D4. |
| • | The APP Angle is 9-99%. |
| • | The engine is running greater than 475 RPM for more than 7 seconds. |
| • | The 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.
-
This step tests for an open in circuit 1694 or a faulty transfer case switch.
-
This step tests for a short to ground in circuit 1694.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 |
Important: Before clearing the DTCs, 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 PCM. Does the 4WD LOW on the scan tool display Disabled when 4WD HIGH is selected and Enabled when 4WD LOW is selected? | -- | Go to Diagnostic Aids | |||||
Is the J 39200 DMM reading within the specified value when 4WD LOW is selected. | 0-20 Ω | |||||||
Select 4WD High with the shift lever, (the drive wheels may have to be rotated). Is the J 39200 DMM reading greater than specified value when 4WD High is selected? | 50k Ω | |||||||
5 | Inspect or repair circuit 1694 for an open. Refer to General Electrical Diagnosis Procedures. Did you find the condition? | -- | ||||||
6 | Inspect and repair circuit 1694 for a short to ground. Refer to General Electrical Diagnosis Procedures. Did you find the condition? | -- | ||||||
7 | Replace the transfer case switch. Refer to Transfer Case Switch Replacement. Is the replacement complete? | -- | -- | |||||
8 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the replacement complete? | -- | -- | |||||
9 | In order to verify your repair, perform the following procedure:
Has the test run and passed? Important: After the repair has been made, a harsh shift condition may exist. This condition is caused by the steady state adapts. To clear the steady state adapt cells, select clear taps. | 4WD High | System OK |
