DTC P1875 4WD Low Switch Circuit Electrical. Isuzu S/T Isuzu

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 1997 🢒 S/T Isuzu - 2WD 🢒 DTC 🢒 DTC P1875 4WD Low Switch Circuit Electrical

Circuit Description

Although 4WD is not applicable to the GMT150, a 4WD low circuit exists as part of the instrument panel extension harness and instrument panel harness. Circuit 1694 extends from VCM terminal C4-23 to the instrument panel harness connector (terminal C). This circuit has the potential, if grounded, to set a DTC P1875. Even though the possibility of this occurring is very remote, a diagnostic check must be included in the event this DTC sets.

When the VCM detects a continuous 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 lb ft.

•	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 the following fail condition occurs:

-	Four-wheel drive low is stuck ON (circuit 1694 is grounded) for 5 seconds. The TCC slip speed is -3000 to -50 RPM. The speed ratio is 0.8-1.2. (The speed ratio is the engine speed divided by transmission output speed).

Action Taken When the DTC Sets

•	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. Look for the following conditions:

-	A bent terminal

-	A backed out terminal

-	A damaged terminal

-	A grounded terminal

-	Poor terminal tension

-	A chafed wire

-	A broken wire inside the insulation

•	When diagnosing for an intermittent short 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 chart.

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

DTC P1875 Four-Wheel Drive Low Circuit Malfunction

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to OBD System Check
2	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, then clear the DTC. Turn the ignition switch OFF. Disconnect the C4 (black) VCM connector. Using the J 39200 DVOM and J 35616-A Connector Test Adapter Kit, measure the resistance between C4-23 and a known good ground. Is the resistance measured less than the specified value?	1000 ohms	Go to Step 3	Go to Diagnostic Aids
3	Inspect circuit 1694 for a short to ground. Repair the circuit if necessary. Refer to Electrical Diagnosis, Section 8A. Did you find and correct a problem?	--	Go to Step 5	Go to Step 4
4	Replace the VCM. Refer to VCM Replacement, Section 6. Is the replacement complete?	--	Go to Step 5	--
5	In order to verify your repair, perform the following procedure: Select DTC. Select Clear Info. 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