DTC P1875 4 Wheel Drive Switch Circuit. Isuzu Isuzu

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 1997 🢒 Isuzu - N Series 🢒 DTC 🢒 DTC P1875 4 Wheel Drive Switch Circuit

Automatic Transmission Components Gas
Automatic Transmission Controls Schematics 5.7 and 7.4 L Gas Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The 4WD low circuit consists of a 4WD indicator assembly, a selector quadrant switch, and wiring. When the operator moves the selector quadrant switch to 4 Low, the 4WD indicator lamp illuminates, and circuit 1694 voltage to the Vehicle Control Module (VCM) changes from B+ to zero. The 4WD low switch signal is used to correct the transmission output speed signal to the VCM. This signal compensates for transfer case gear reduction. The VCM uses the transmission output speed signal in order to adjust shift points, line pressure, and TCC scheduling.

If the VCM detects a continuous open or short to ground in the 4WD low 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 TP Sensor DTCs P0121, P0122 or P0123.

•	No OSS DTC P0502.

•	No 1-2 SS Valve DTC P0753.

•	No 2-3 SS Valve DTC P0758.

•	No TFP Val. Position Sw. DTC P1810.

•	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).

•	The shift solenoid performance counters are zero.

•	All of the above conditions are met and one of the following fail conditions are true:

-	Four wheel drive low circuit is closed (grounded) for more than 2 seconds with a transfer case ratio of 0.95-1.05:1.

-	The four wheel drive low circuit is open for 3 seconds with a transfer case ratio of 2.66-2.76:1 in any two gears for 1 occurrence.

Action Taken When the DTC Sets

•	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.

•	For California emissions vehicles, the VCM illuminates the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the DTC

For California emissions vehicles, 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 problems:

-	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, 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.

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

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

Go to Step 2

Go to Powertrain On Board Diagnostic (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.