Symptom-Based Diagnosis
Symptoms - Computers and Control SystemImportant Preliminary Inspections Before Starting
Perform Diagnostic System Check - Computers and Control Systems before using the symptom tables, and verify that all of the following are true:
- The powertrain control module (PCM) and malfunction indicator lamp (MIL) are operating correctly.
- There are no DTCs stored.
- Verify that the engine is not in a torque reduction mode. The PCM turns certain injectors OFF or reduces the engine timing when the PCM detects an over torque condition or an abusive maneuver.
- Verify that the engine coolant temperature (ECT) is not above 130 °C (266 °F). This condition causes the PCM to operate in Engine Coolant Over Temperature-Fuel Disabled Mode. While in Engine Coolant Over Temperature-Fuel Disabled Mode, the PCM turns the fuel OFF to four cylinders at a time in order to keep engine temperatures from reaching damaging levels. The driver may perceive Engine Coolant Over Temperature as a lack of power, miss, or rough idle. If the vehicle is operating in Engine Coolant Over Temperature-Fuel Disabled Mode, refer to Engine Overheating In Cooling Systems for diagnosis.
- The scan tool data is within the normal operating range, refer to Scan Tool Data List. Scan Tool Data List
- Verify the customer concern and locate the correct symptom in the table of contents. Inspect the items indicated under that symptom.
Visual/Physical Inspection
Several of the symptom procedures ask for a careful visual and physical inspection. This step is extremely important. The visual and physical inspection can lead to correcting a problem without further inspections, and can save valuable time. Ensure that:
- The PCM grounds are clean, tight, and in the proper location.
- The vacuum hoses are not split or kinked, and properly connected, as shown on the Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction.
- The mass air flow (MAF) sensor is properly installed. The arrows on the plastic portion of the sensor must point toward the engine.
- The air intake ducts are not collapsed or damaged.
- There are no leaks at the throttle body mounting area, the MAF sensor, or the intake manifold sealing surfaces.
- The ignition wires are not cracked, brittle, or carbon tracked.
- The engine harness wiring and terminals are properly connected and are not pinched or cut.
Use the following tables when diagnosing a symptom complaint:
- Intermittent Conditions
Intermittent Conditions
- Hard Start
Hard Start
- Surges/Chuggles
Surges and/or Chuggles
- Lack of Power, Sluggishness, or Sponginess
Lack of Power
- Detonation/Spark Knock
Detonation - Pings, Spark Knock
- Hesitation, Sag, Stumble
Hesitation, Sag, Stumble
- Cuts Out, Misses
Cuts Out, Misses
- Poor Fuel Economy
Poor Fuel Economy
- Poor Fuel Fill Quality
Poor Fuel Fill Quality
- Rough, Unstable, or Incorrect Idle and Stalling
Rough, Unstable, or Incorrect Idle, Stalling
- Dieseling, Run-On
Dieseling, Run on
- Backfire
Backfire
- Engine Cranks but Does Not Run
Engine Cranks But Does Not Run
- Malfunction Indicator Lamp (MIL) Inoperative
Malfunction Indicator Lamp (MIL) Inoperative
- Malfunction Indicator Lamp (MIL) Always On
Malfunction Indicator Lamp (MIL) "ON" Steady