TB4 - Cycle the Appropriate Circuit: (4X4 Low or Transmission)

- Key "OFF".

- Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.

- Install breakout box, leave PCM disconnected.

- Key "ON", engine "OFF".

- For 4x4 Low circuit:

- Measure voltage between test pin 12 and test pin 40/60 at the breakout box while moving the 4x4 select lever between 4x2 and 4x4 Low several times.

- For Transmission Control Switch (TCS) circuit:

- Measure voltage between test pin 41 and test pin 40/60 at the breakout box while cycling the transmission control switch several times.

- Does the voltage cycle?

Yes -- Replace PCM. Remove breakout box. Rerun quick test. Quick Test Appendix (Detailed Testing Instructions)

No -- For a driveability symptom only: Go to TB7. TB7 - Check Output Driver Signal

For a DTC: Go to TB5. TB5 - Check Harness Circuit(s) For Short to Ground