System Inspection

Cruise Control Diagnosis




Circuit Description
The stepper motor cruise module communicates with the PCM over three circuits (cruise engaged, cruise disabled and VSS output). The cruise enable status tells the PCM if the cruise control system is enabled. The VSS output is the speed signal from the vehicle speed sensor through the PCM and used by the cruise control module. The cruise disable line allows the PCM to disable cruise under the various conditions described below:
- No active TP DTC's
- No active Injector Control DTC's
- No active CKP DTC's
- No active VSS DTC's
- No active System Voltage DTC's
- Engine is not running.
- Transmission is in park, neutral or reverse (auto trans.).
- Transmission is out of gear (manual trans.).
- Safety fuel cut-off is active.

If the PCM detects any one of the above conditions, it will interrupt the ground at the cruise disable input circuit and disable the cruise control.

Diagnostic Aids
- This table will not diagnose any cruise control system circuits other than those connected to the PCM. For diagnosis of the remaining circuits, refer to Wiring Repairs.
- The cruise control system may disable if actual speed is less than 24 kph (15 mph) than commanded vehicle speed; i.e. towing a trailer, or climbing a steep grade.
- Minimum vehicle speed for setting the cruise control system is 40 kph (25 mph). An intermittent may be caused by any of the following conditions:
- A poor connection
- Rubbed through wire insulation
- A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs.

Steps 1 - 4:

Steps 5 - 8:

Steps 9 - 11:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
3. The cruise speed set has to be above the minimum speed (25 mph/40 kph) required for cruise operation. Drive vehicle in an area where enough room is allowed for cruising.
4. If the vehicle was in the enabling criteria for cruise operation, the PCM should have read stepper cruise Engaged even if cruise was not requested. The Cruise Engaged circuit provides a ground to the cruise control module. This step checks for an open or shorted cruise engage circuit.
6. At this point, the PCM is allowing cruise operation and the cruise module is telling the PCM that the cruise is engaged. If the vehicle will not maintain the set speed, then the malfunction is in the cruise control module or is a throttle linkage problem.
10. The replacement PCM must be programmed and the crankshaft position system variation procedure must be preformed. Refer to the latest Isuzu Technical Communication System (ITCS) procedure for PCM reprogramming and also refer to the Crankshaft Position System Variation Procedure.