Part 1

Symptoms - Engine Controls

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Symptoms Description

Symptoms covers conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under Additional Symptoms Testing. Perform the Symptoms Testing before using the Additional Symptoms Testing.

Symptoms Definition

Backfire
- The fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.

Cuts Out, Misses
- A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or at low speed.

Detonation/Spark Knock
- A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.

Dieseling, Run-On
- The engine continues to run after the key is turned OFF, but runs very rough.

Engine Control Module (ECM) Commanded Reduced Engine Power
- The ECM illuminates the Reduced Engine Power lamp and will limit engine power under potential engine/vehicle damaging or emissions related conditions. A DTC may not be set.

Fuel Odor
- A noticeable smell of unburned fuel.

Hard Start
- The engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stall.

Hesitation, Sag, Stumble
- A momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop. This condition may cause the engine to stall in severe conditions.

Lack of Power, Sluggishness, or Sponginess
- The engine delivers less than expected power. Little or no increase in vehicle speed when the accelerator pedal is pushed down part way.

Poor Fuel Economy
- Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Rough, Unstable, or Incorrect Idle and Stalling
- The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary. Either condition may be severe enough to stall the engine.

Surges/Chuggles
- An engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.

Symptoms Verification

Before using the Symptom tables, perform the following inspections:

* Verify that the malfunction indicator lamp (MIL) is operating correctly. Use the scan tool to command the lamp ON and OFF.

* Verify that there are no DTCs that are stored.

* Verify that the scan tool data is within a normal operating range. Refer to Control Module References Programming and Relearning for scan tool information.

* Verify the customer concern.

* Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition.

Identifying Intermittent Conditions

Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movements of a component. Refer to the following for a list of issues that may cause an intermittent condition:

* Moisture and water intrusion in connectors, terminals, and components

* Incomplete connector mating

* Poor terminal contact

* High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component.

* Harness that is too short or tight

* Wire insulation that is chaffed or cut

* High or low ambient temperature

* High or low engine coolant temperatures

* High underhood temperatures

* Heat build up in component or circuit due to circuit resistance, poor terminal contact, or high electrical load

* High or low system voltage

* High vehicle load conditions

* Rough road surfaces

* Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge

* Incorrect installation of aftermarket, add on accessories

Visual/Physical Check

* Verify that the control module grounds are clean, tight, and correctly located.

* Verify that the vacuum hoses are not split or kinked, and are properly connected, as shown on the Vehicle Emission Control Information label.

* Verify that the air filter is clean and free from restrictions.

* Verify that there is no water intrusion in connectors terminals and components.

* Inspect the air intake ducts for the following conditions:

- Collapsed

- Damaged areas

- Looseness

- Incorrect installation

- Leaking

* Inspect for air leaks at the throttle body mounting area, the mass air flow (MAF) sensor and intake manifold sealing surfaces.

* Inspect the wiring harness for the following conditions:

- Poor connections

- Pinches

- Cuts

* Inspect for loose, damaged, unseated, or missing sensors/components.

* Inspect the terminals for corrosion and correct contact.