NOTE: Chrysler Motors recommends using DRB-II to diagnose system. Voltmeter usage has limited diagnostic capabilities but can be used if DRB-II is not available or if working on a Mitsubishi Motors vehicle.

The Engine Control Unit (ECU) monitors several different engine control system circuits. If an abnormal input signal occurs, a fault code is stored in ECU memory and given a fault code number. Each circuit has its own fault number and message. A specific fault code indicates a particular system failure, but it DOES NOT indicate that cause of failure is necessarily within system. A fault code DOES NOT condemn any specific component; it simply points out a probable malfunctioning area. If a critical fault code is set, the ECU will turn on CHECK ENGINE light. All fault codes except speed sensor are considered critical.

Fault codes can be confirmed by using a voltmeter on Chrysler Motors and Mitsubishi models or Chrysler's Diagnostic Readout Box (DRB-II) on Chrysler Motors vehicles. See ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) or ENTERING ON-BOARD DIAGNOSTICS (USING DRB-II) . By using the DRB-II, the self-diagnostic capabilities of this system can simplify testing and reduce diagnostic time.

System malfunctions encountered are identified as either hard failures or intermittent failures as determined by the ECU.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

System Diagnosis: Notes

Use the Manual With the Right Hardware

When to See a Mechanic

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