- Symptoms - Engine Controls
Symptoms - Computers and Control Systems.
Important Preliminary Inspections Before Starting
Before using the Symptom tables, perform the following:
* Perform Diagnostic System Check - Vehicle and verify all of the following items:
- Ensure that the engine control module and malfunction indicator lamp (MIL) are operating correctly.
- Ensure that there are no diagnostic trouble codes (DTCs) that are stored.
- Scan tool data is within a normal operating range. Refer to Scan Tool Data List. Scan Tool Data List Initial Inspection and Diagnostic Overview
* Verify the customer concern.
* Perform the Visual/Physical Inspection. 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.
* Locate the correct symptom. Perform the tests and inspections associated with the symptom.
Identifying Intermittent Conditions
Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movement of a component. Refer to the following for a list to help determine an intermittent condition:
* Moisture, and water intrusion in connectors, terminals, and components
* Connector mating
* 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 located too tight, or chaffed circuits
* 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 surface
* Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge
* Incorrect installation of non-factory, aftermarket, and after factory add on accessories
If an intermittent is determined, Refer to Testing for Intermittent Conditions and Poor Connections for specific strategies in diagnosing intermittent conditions. Component Tests and General Diagnostics
Visual/Physical Check
Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:
* The PCM harness connectors
* The electrical center fuse/relay cavities
* The component terminals
* The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.
Several of the symptom procedures call for a careful visual and physical inspection. This can lead to correcting a condition without further tests and can save time. This inspection should include the following areas:
* Ensure that the control module grounds are clean, tight, and correctly located. Refer to Master Electrical Component List and Power and Grounding Connector End Views.
* Inspect vacuum hoses for splits, kinks, and proper connections, as shown on the Vehicle Emission Control Information label. Inspect thoroughly for any type of a leak or a restriction. Refer to Emission Hose Routing Diagram (L26, NU3) and Evaporative Emissions Hose Routing Diagram.
* Inspect for a dirty or restricted air filter.
* Inspect for water intrusion in the mass air flow/intake air temperature (MAF/IAT) sensor connector, heated oxygen sensor (HO2S) connectors, control module connectors or any other harness connectors.
* Inspect the air intake ducts, particularly between the MAF sensor and the throttle body 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 terminals for corrosion and correct contact.
Symptoms
Hard Start
- Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately stalls.
Surges/Chuggles
- Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down without a change in the accelerator pedal position.
Lack of Power, Sluggishness, or Sponginess
- The engine delivers less than expected power. Little increase in speed, or a total lack of acceleration when the accelerator pedal is pushed down part way.
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.
Hesitation, Sag, Stumble
- 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 sign. This condition may cause the engine to stall if severe enough.
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.
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 may vary in speed. Either condition may be severe enough to stall the engine.
Dieseling, Run-On
- The engine continues to run after the key is turned OFF, but runs very rough. If the engine runs smooth, inspect the ignition switch and the ignition switch adjustment.
Backfire
- Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Use the symptoms in order to isolate possible systems that are associated with the condition.