DTC P1875 4WD Low Switch Circuit Electrical. GMC Truck Yukon

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1997 🢒 Yukon - 4WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L60-E 🢒 DTC P1875 4WD Low Switch Circuit Electrical

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OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The 4WD low circuit consists of a transfer case switch, a front axle switch and a front axle actuator. When 4WD low is engaged, circuit 1694 voltage to the VCM changes from ignition voltage to zero. The 4WD low switch signal corrects the transmission output speed signal to the VCM. This signal 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 A DTC.

Conditions for Setting the DTC

•	No TP DTCs P0121, P0122, or P0123

•	No VSS Assy. DTC P0502

•	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 8 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 TFT is 20-120°C (68-248°F).

•	All of the above conditions are met and either of the following fail conditions occurs:

-	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 commands a normal shift pattern (not a 4WD low shift pattern).

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

Conditions for Clearing the MIL/DTC

•	The VCM turns OFF the MIL after three consecutive ignition cycles 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 conditions:

•	A bent terminal

•	A backed out terminal

•	A damaged terminal

•	Poor terminal tension

•	A chafed wire

•	A broken wire inside the insulation

•	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 a short to ground in circuit 1694.

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

DTC P1875 4 Wheel Drive Low Circuit Malfunction

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain OBD System Check

Install the scan tool.
With the engine OFF, turn the ignition switch to the RUN position.

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 data.

Record the DTC Freeze Frame and Failure Records.
Place the transmission in Neutral.
Select 4HI on the transfer case selector switch.
Select 4LO on the transfer case selector switch.

Does the scan tool 4WD Low display No when you select 4HI, then Yes when you select 4LO?

Go to Diagnostic Aids

Go to Step 3

Turn the ignition switch OFF.
Disconnect the transfer case switch connector.
Turn the ignition switch to the RUN position.

Does the scan tool 4WD Low indicate Yes?

Go to Step 6

Go to Step 4

Connect terminal B of the transfer case switch connector to a known good ground.
Observe the scan tool 4WD Low.

Does 4WD Low indicate Yes when circuit 1694 is grounded?

Go to Step 5

Go to Step 7

Replace the transfer case selector switch.

Refer to Transfer Case Selector Switch Replacement, Section 7.

Is the replacement complete?

Go to Step 9

Inspect circuit 1694 for a short to ground.
Repair the circuit if necessary.

Refer to Electrical Diagnosis, Section 8.

Did you find a problem?

Go to Step 9

Go to Step 8

Inspect circuit 1694 for an open.
Repair the circuit if necessary.

Refer to Electrical Diagnosis, Section 8.

Did you find a problem?

Go to Step 9

Go to Step 8

Replace the VCM.

Refer to VCM Replacement, Section 6.

Is the replacement complete?

Go to Step 9

In order to verify your repair, perform the following procedure:

Select DTC.
Select Clear Info.
Operate the vehicle under the following conditions:

•	Select 4LO on the selector switch.

•	Drive the vehicle in 4th gear with the TCC ON.

•	The speed ratio must be 2.5-2.9 for 5 seconds.

•	Select 2HI or 4HI on the selector switch.

•	Drive the vehicle in 4th gear with the TCC ON.

•	The speed ratio must be 0.8-1.2 for 5 seconds.

Select Specific DTC. Enter DTC P1875.

Has the test run and passed?

System OK

Begin the diagnosis again. Go to Step 1