How to troubleshoot car problem?

Do not attempt to diagnose a Drivability Symptoms without having a logical plan to use to determine which Engine Control system is the cause of the symptom - this plan should include a way to determine which systems do not have a problem! Drivability symptom diagnosis is a part of an organized approach to problem solving and repair.

Drivability Symptom Index Table

To use this list, locate the symptom that matches a particular problem and refer to the areas to test. The items listed under each symptom may not apply to all models, engines or vehicle systems. The repair steps indicate what vehicle component or system to test.

NOTE

The Drivability Symptoms in this list are intended to be generic. While they apply to most vehicles, some vehicles may not have all of the components listed. Refer to other Chilton repair manuals and electronic media for specific tests.

Symptom Test Table

Symptom Description	Suggested Areas to Test
Test 1 - No Start, Hard Start Condition l No Crank l Hard Start, Long Crank, Erratic Crank l Stall After Start l No Start, Normal Crank l No Start, MIL is off (if the VREF shorts to ground)	- Check battery, battery circuits to starter- Check for a damaged flywheel, engine compression, base timing and minimum air rate- Check for a failed fuel pump relay- Check for distributor rotor "punch-through"- Check for a faulty ignition control module (ICM)- Check for a VREF circuit shorted to ground- Check SKIM (security system) with a Scan Tool
Test 2 - Rough Idle or Stalls Condition l Low or slow idle speed l Fast idle speed l Hunting or rolling idle speed l Slow return to idle speed l Stalls or almost stalls	- Check for engine vacuum leaks- Check the condition of the PCV valve and lines- Check for excessive carbon buildup- Check for a restricted exhaust (in Section 2)- Check base idle speed, check for low fuel pressure- Check the throttle linkage for sticking or binding
Test 3 - Runs Rough Condition l At idle speed l During acceleration l At cruise speed l During deceleration	- Check for engine vacuum leaks at intake manifold- Check condition of ignition secondary components- Check base timing and idle speed settings- Check for low or high fuel pressure- Check for dirty, leaking or shorted fuel injectors- Check for excessive carbon buildup on valves
Test 4 - Cuts-out, Misses Condition l At idle speed l During acceleration l At cruise speed l During deceleration	- Check for engine vacuum leaks at intake manifold- Check condition of ignition secondary components- Check that spark timing advance is available- Check for low or high fuel pressure- Check for dirty, leaking or shorted fuel injectors- Check for excessive carbon buildup on valves
Test 5 - Bucks, Jerks Condition l During acceleration l At cruise speed l During deceleration	- Check for engine vacuum leaks at intake manifold- Check condition of ignition secondary components- Check that spark timing advance is available- Check for low or high fuel pressure- Check for dirty, leaking or shorted fuel injectors- Check operation of the TCC solenoid, brake switch

Symptom Diagnosis Test 1 - No Start, Hard Start Condition

NOTE

If there is no spark output or fuel pressure available, check for a failed fuel pump relay, no power to the PCM, or loss of the ignition reference signal to the PCM.

Preliminary Checks

Prior to starting this symptom test routine, inspect these underhood items:

Check battery charge and condition, starter current draw.

Verify the starter relay operation and that the engine cranks (turns over).

Verify the check engine light (MIL) operation - if it does not activate, check the PCM power and ground circuits, and check for 5v supply at the MAP or TP sensor.

Check Air Intake system for restrictions (inspect air inlet tubes, air filter for dirt, etc.).

Check the status of the Smart Key Immobilizer System (SKIM) with the Scan Tool.

Test 1 Chart

Step	Action	Yes	No
1	Step Description: No Start Condition Only » Check battery cables, state of charge. » If the engine does not rotate, inspect for a locked engine (hydrostatic lockup condition). » Does the engine crank normally-	Go to Step 2.	Repair the fault in the battery, starter, or Base Engine. Retest for the symptom when all repairs are done.
2	Step Description: Check the Fuel System » Verify that the pump operates at key on. » Check the fuel pump relay operation. If the relay does not operate, check for blown fuse. » Inspect pump for a leak-down condition » Test fuel pressure, volume and quality. » Test the operation of the fuel regulator. » Are there any faults in the Fuel system-	Make needed repairs.	Go to Step 3.
3	Step Description: Check the Ignition System » Inspect ignition secondary components for damage (look for rotor "punch-through"). » Inspect the coils for signs of spark leakage at coil towers or primary connections. » Check the spark output with a spark tester. » Test Ignition system with an engine analyzer. » Are there any faults in the Ignition system-	Make repairs to the Ignition system. Then retest the symptom.	Go to Step 4.
4	Step Description: Check the Exhaust System » Check Exhaust system for leaks or damage. » Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). » Are there any faults in the Exhaust system-	Make repairs to the Exhaust system. Then retest the symptom.	Go to Step 5.
5	Step Description: Check the MAP Sensor » Disconnect the MAP sensor and attempt to start the engine. » Does the engine start and run normally-	Replace the MAP sensor. Retest for the symptom when repairs are completed.	Go to Step 6.

No Start, Hard Start Condition (Continued)

Test 1 Chart (Continued)

Step	Action (Hard Start Only)	Yes	No
6	Step Description: Check for a Hot Engine » Check for signs of an engine overheating condition related to a Hard Start Symptom. » Does the engine appear to be overheated-	Make the repairs to correct the hot engine and then retest for the symptom when done.	Go to Step 7.
7	Step Description: Check ECT Sensor PID » Connect a Scan Tool and turn the key to on. » Read the ECT sensor (compare to chart). » Has the ECT sensor shifted out of range-	Replace the ECT sensor. Then retest for the symptom when all repairs are completed.	Go to Step 8.
8	Step Description: Check the PCV System » Inspect the PCV system components for broken parts or loose connections. » Test the operation of the PCV valve. » Are there any faults in the PCV system-	Repair the PCV system. Refer to the PCV system tests. Retest the symptom when all repairs are done.	Go to Step 9.
9	Step Description: Check the EVAP System » Inspect for damaged or disconnected EVAP system components. » Inspect for a fuel saturated charcoal canister. » Are there any faults in the EVAP system-	Refer to the EVAP system tests in this manual. Retest for the symptom when all repairs are completed.	Go to Step 10.
10	Step Description: Test the Base Engine » Check the engine compression. » Test valve timing and timing chain condition. » Check for a worn camshaft or valve train. » Check for any large intake manifold leaks. » Are there any faults in the Base Engine-	Repair the Base Engine.Refer to the Base Engine Tests in this manual. Retest symptom when done.	Return to Step 2 to repeat the test steps in this series to locate and repair the "No Start, Hard Start" condition.

Symptom Diagnosis Test 2 - Rough, Low Or High Idle Speed Condition

NOTE

If the vehicle has a rough idle and the base timing, idle speed and the IAC (or AIS) motor operates properly, check the engine for excessive carbon buildup.

Preliminary Checks

Prior to starting this symptom test routine, inspect these underhood items:

All related vacuum lines for proper routing and integrity.

All related electrical connectors and wiring harnesses for faults (Wiggle Test).

Check the throttle linkage for a sticking or binding condition.

Air Intake system for restrictions (air inlet tubes, dirty air filter, etc.).

Search for any technical service bulletins related to this symptom.

Turn the key to off. Unplug the MAP sensor connection and restart the engine to recheck for the idle concern. If the condition is gone, replace the MAP sensor.

Test 2 Chart

Step	Action	Yes	No
1	Step Description: Verify the rough idle or stall » Does the engine have a warm engine rough idle, low idle or high idle condition in P or N-	Go to Step 2.	Fault is intermittent. Return to the Symptom List and select another fault.
2	Step Description: Verify idle speed & timing » Verify the base timing is within specifications » Verify that the base idle speed is set properly » Are the timing and idle speed set properly-	Go to Step 3.	Set the base idle speed and timing to the specifications and then retest for the symptom.
3	Step Description: Check AIS / IAC Operation » Check the AIS or IAC motor operation » Inspect the AIS/IAC housing in throttle body for restricted passages. Clean as needed. » Set the parking brake, block the drive wheels and turn the A/C off. Install the Scan Tool. » IAC Motor Tester - Turn the key off and then connect the IAC tester to the IAC valve. » Start the engine and use the IAC tester to extend and retract the IAC valve. » ATM Test - Start the engine. Use the tool to change the speed from min-idle to 1500 rpm. » Did the idle speed change as commanded-	Install an Aftermarket Noid light and check the operation of the PCM and AIS or IAC motor circuits.Check the motor for signs of open or shorted circuits.Replace the IAC motor or PCM as needed or make repairs to the IAC motor wiring.If all are okay, go to Step 4.	If the AIS/IAC motor passages are clean and engine speed did not change as described when the AIS/IAC motor was extended and retracted, replace the AIS/IAC motor.Then retest for the condition.
4	Step Description: Check/compare PID values » Connect Scan Tool & turn off all accessories. » Start the engine and allow it to fully warmup. » Monitor all related PIDs on the Scan Tool. » Verify the P/N switch input in gear and Park. » Check the O2S operation with a Lab Scope. » Are all PIDs within normal range-	Go to Step 5.Note: An IAC motor count of over 80 indicates the pintle is extended and an IAC count of (0) indicates the pintle is retracted.	One or more of the PIDs are out of range when compared to "known good" values. Make repairs to the system that is out of range, then retest for the symptom.
5	Step Description: Check the Ignition System » Inspect the coils for signs of spark leakage at coil towers or primary connections. » Check the spark output with a spark tester. » Test Ignition system with an engine analyzer. » Were any faults found in the Ignition system-	Make repairs as needed	Go to Step 6.
6	Step Description: Check the Fuel System » Inspect the Fuel delivery system for leaks. » Test the fuel pressure, quality and volume. » Test the operation of the pressure regulator. » Were any faults found in the Fuel system-	Make repairs as needed	Go to Step 7.
7	Step Description: Check the Exhaust System » Check Exhaust system for leaks or damage. » Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). » Were any faults found in Exhaust System-	Make repairs to the Exhaust system. Then retest the symptom.	Go to Step 8.

Test 2 Chart (Continued)

Step	Action	Yes	No
8	Step Description: Check the PCV System » Inspect the PCV system components for broken parts or loose connections. » Test the operation of the PCV valve. » Were any faults found in the PCV system-	Make repairs to the PCV system. Refer to the PCV system tests. Then retest for the condition.	Go to Step 9.
9	Step Description: Check the EVAP System » Inspect for damaged or disconnected EVAP system components or a saturated canister. » Were any faults found in the EVAP system-	Make repairs to EVAP system (use the EVAP tests in this manual). Retest for the condition.	Go to Step 10.
10	Step Description: Check the Base Engine » Test the engine compression. » Test valve timing and timing chain condition. » Check for a worn camshaft or valve train. » Check for any large intake manifold leaks. » Were any faults found in the Base Engine-	Make repairs as needed to the Base Engine. Refer to the Base Engine tests. Then retest for the condition when repairs are completed.	Go to Step 2 and repeat the tests from the beginning to locate and repair the cause of the "Rough, Low or High Idle Speed" condition.

Symptom Diagnosis Test 3 - Runs Rough Condition
Preliminary Checks

Prior to starting this symptom test routine, inspect these underhood items:

All related vacuum lines for proper routing and integrity

Air Intake system for restrictions (air inlet tubes, dirty air filter, etc.)

Search for any technical service bulletins related to this symptom.

Test 3 Chart

Step	Action	Yes	No
1	Step Description: Verify engine runs rough » Start the engine and allow it to idle in P or N. » Does the engine run rough when warm in Park or Neutral position-	Check for any stored codes. If codes are set, repair codes and retest. If no codes are set, go to Step 3.	Go to Step 2.
2	Step Description: Condition does not exist! » Inspect various underhood items that could cause an intermittent Runs Rough condition (i.e., dirt in the throttle body, vacuum leaks, IAC motor connections, etc.). » Were any problems located in this step-	Correct the problems. Do a PCM reset and engine "idle relearn" procedure. Then verify the "runs rough" condition is repaired.	The problem is not present at this time.It may be an intermittent problem.
3	Step Description: Check/compare PID values » Connect a Scan Tool to the test connector. » Turn off all accessories. » Start the engine and allow it to fully warmup. » Monitor all related PIDs on the Scan Tool. » Were all PIDs within their normal range-	Go to Step 4.Note: The IAC motor should read from 5-50 counts. Check the LONGFT reading for a large shift into the negative range (due to a rich condition).	One or more of the PIDs are out of range when compared to "known good" values. Make repairs to the system that is out of range, then retest for the symptom.

Test 3 Chart (Continued)

Step	Action	Yes	No
4	Step Description: Check the Ignition System » Inspect the coils for signs of spark leakage at coil towers or primary connections. » Check the spark output with a spark tester. » Test Ignition system with an engine analyzer. » Were any faults found in the Ignition system-	Make repairs as needed	Go to Step 5.
5	Step Description: Check the Fuel System » Inspect the Fuel delivery system for leaks. » Test the fuel pressure, quality and volume. » Test the operation of the pressure regulator. » Were any faults found in the Fuel system-	Make repairs as needed	Go to Step 6.
6	Step Description: Check the Exhaust System » Check Exhaust system for leaks or damage. » Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). » Were any faults found in Exhaust System-	Make repairs to the Exhaust system. Then retest the symptom.	Go to Step 7.
7	Step Description: Check the PCV System » Inspect the PCV system components for broken parts or loose connections. » Test the operation of the PCV valve. » Were any faults found in the PCV system-	Make repairs to the PCV system. Refer to the PCV system tests. Then retest for the condition.	Go to Step 9.
8	Step Description: Check the EVAP System » Inspect for damaged or disconnected EVAP system components or a saturated canister. » Were any faults found in the EVAP system-	Make repairs to EVAP system (use the EVAP tests in this manual). Retest for the condition.	Go to Step 10.
9	Step Description: Check Engine Condition » Test the engine compression. » Test valve timing and timing chain condition. » Check for a worn camshaft or valve train. » Check for any large intake manifold leaks. » Were any faults found in the Base Engine-	Make repairs as needed to the Base Engine. Refer to the Base Engine tests. Then retest for the condition when repairs are completed.	Return to Step 2 and repeat the tests from the beginning to locate and repair the cause of the "Runs Rough" condition.

Fig. Example EVAP System

Symptom Diagnosis Test 4 - Cuts-Out Or Misses Condition
Preliminary Checks

Prior to starting this symptom test routine, inspect these underhood items:

All related vacuum lines for proper routing and integrity

Search for any technical service bulletins related to this symptom.

Test 4 Chart

Step	Action	Yes	No
1	Step Description: Verify Cuts-out condition » Start the engine and attempt to verify the Cuts-out or misses condition. » Does the engine have a cuts-out condition-	Check for any stored codes. If codes are set, repair codes and retest. If no codes are set, go to Step 3.	Go to Step 2.
2	Step Description: Condition does not exist! » Inspect various underhood items that could cause an intermittent Cuts-out condition (i.e., EVAP, Fuel or Ignition system components). » Were any problems located in this step-	Correct the problems. Do a PCM reset and "Fuel Trim Relearn" procedure. Then verify condition is repaired.	The problem is not present at this time.It may be an intermittent problem.
3	Step Description: Check/compare PID values » Connect a Scan Tool to the test connector. » Turn off all accessories. » Start the engine and allow it to fully warmup. » Monitor all related PIDs on the Scan Tool (i.e., ECT IAC Counts and LONGFT at idle). » Were all PIDs within their normal range-	Go to Step 4.Note: The IAC motor should be from 5-50 counts. Watch fuel trim (%) for a large shift into the negative (-) range (due to a rich condition).	One or more of the PIDs are out of range when compared to "known good" values. Make repairs to the system that is out of range, then retest for the symptom.

Test 4 Chart (Continued)

Step	Action	Yes	No
4	Step Description: Check the Ignition System » Inspect the coils for signs of spark leakage at coil towers or primary connections. » Check the spark output with a spark tester. » Test Ignition system with an engine analyzer. » Were any faults found in the Ignition system-	Make repairs as needed	Go to Step 5.
5	Step Description: Check the Fuel System » Inspect the Fuel delivery system for leaks. » Test the fuel pressure, quality and volume. » Test the operation of the pressure regulator. » Were any faults found in the Fuel system-	Make repairs as needed	Go to Step 6.
6	Step Description: Check the Exhaust System » Check Exhaust system for leaks or damage. » Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). » Were any faults found in Exhaust System-	Make repairs to the Exhaust system. Then retest the symptom.	Go to Step 7.
7	Step Description: Check the PCV System » Inspect the PCV system components for broken parts or loose connections. » Test the operation of the PCV valve. » Were any faults found in the PCV system-	Make repairs to the PCV system. Refer to the PCV system tests. Then retest for the condition.	Go to Step 8.
8	Step Description: Check the EVAP System » Inspect for damaged or disconnected EVAP system components » Check for a saturated EVAP canister. » Were any faults found in the EVAP system-	Make repairs to EVAP system (use the EVAP tests in this manual). Retest for the condition.	Go to Step 9.
9	Step Description: Check the AIR system » Inspect AIR system for broken parts, leaking valves or disconnected hoses (see graphic). » Test the operation of Secondary AIR system. » Were any faults found in the AIR system-	Make repairs as needed. Refer to the Secondary AIR system tests. Retest for the condition.	Go to Step 10.
10	Step Description: Check Engine Condition » Test the engine compression. » Test valve timing and timing chain condition. » Check for a worn camshaft or valve train. » Check for any large intake manifold leaks. » Were any faults found in the Base Engine-	Make repairs as needed to the Base Engine. Refer to the Base Engine tests. Then retest for the condition when repairs are completed.	Go to Step 2 and repeat the tests from the beginning to locate and repair the cause of the "Cuts Out or Misses" condition.

Fig. Typical Secondary Air System

Symptom Diagnosis Test 5 - Surge Condition
Preliminary Checks

1. Discuss how the operation of the torque converter clutch (TCC) or air conditioning compressor can affect the "feel" of the vehicle during normal operation.
2. Search for any technical service bulletins related to this symptom.

Test 5 Chart

Step	Action	Yes	No
1	Step Description: Verify the surge condition » Drive the vehicle and attempt to verify that the vehicle surges at cruise speeds. » Does the engine have a surge condition-	Check for any stored codes. If codes are set, repair codes and retest. If no codes are set, go to Step 3.	Go to Step 2.
2	Step Description: Condition does not exist! » Inspect various underhood items that could cause an intermittent surge condition (check for leaks in the MAP sensor vacuum lines). » Were any problems located in this step-	Correct the problems. Do a PCM reset and "Fuel Trim Relearn" procedure. Then verify condition is repaired.	The problem is not present at this time.It may be an intermittent problem.
3	Step Description: Check/compare PID values » Connect a Scan Tool to the test connector. » Start the engine and allow it to fully warmup. » Monitor all related PIDs on Scan Tool (HO2S switching, LONGFT, and the TCC operation) » Compare VSS PID reading to speedometer. » Were all PIDs within their normal range-	Go to Step 4.Note: Verify that the front HO2S responds quickly to throttle changes. Check for silicon contamination on the front HO2S (this can cause a rich A/F signal).	One or more of the PIDs are out of range when compared to "known good" values. Make repairs to the system that is out of range, then retest for the symptom.
4	Step Description: Check the Ignition System » Inspect the coils for signs of spark leakage at coil towers or primary connections. » Check the spark output with a spark tester. » Test Ignition system with an engine analyzer. » Were any faults found in the Ignition system-	Make repairs as needed	Go to Step 5.

Test 5 Chart (Continued)

Step	Action	Yes	No
5	Step Description: Check the Fuel System » Inspect the Fuel delivery system for leaks. » Test the fuel pressure, quality and volume. » Test the operation of the pressure regulator. » Were any faults found in the Fuel system-	Make repairs as needed	Go to Step 6.
6	Step Description: Check the Exhaust System » Check Exhaust system for leaks or damage. » Check the Exhaust system for a restriction using the Vacuum or Pressure Gauge Test (e.g., exhaust backpressure reading should not exceed 1.5 psi at cruise speeds). » Were any faults found in Exhaust System-	Make repairs to the Exhaust system. Then retest the symptom.	Return to Step 2 and repeat the tests from the beginning to locate and repair the cause of the "Surge" condition.