DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to the Powertrain (OBD) System Check

1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

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Go to Step 14

Go to Step 3

Was visual/physical check performed?

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Go to Step 4

Go to Visual /Physical check

If scan tool readings are normal (refer to Typical Scan Values ) and there are no engine mechanical faults, fill fuel tank with a known quality gasoline that has a minimum octane reading of 92 and re-evaluate vehicle performance.

Is detonation present?

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Go to Step 5

Go to Step 14

1. Check Transaxle Range switch circuits; use a scan tool and be sure the scan tool indicates that the vehicle is in drive with gear selector in drive or overdrive.
2. If a problem is found, diagnose and repair Transaxle Range switch as necessary. Refer to 4T80-E Automatic Transaxle Diagnosis.

Was a problem found?

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Go to Step 14

Go to Step 6

1. Check TCC operation. Refer to 4T80-E Automatic Transaxle Diagnosis .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to Step 7

1. Check for obvious overheating problems:

•	Low engine coolant.

•	Restricted air flow to radiator, or restricted water flow through radiator.

•	Inoperative electric cooling fan circuit(s), go to the Cooling Fan Functional Check .

•	Correct coolant solution should be a 50/50 mix of approved antifreeze/coolant and water. Refer to Cooling and Radiator .

•	EGR operation-refer to DTC P0401 .

2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to Step 8

1. Check fuel pressure. Refer to Fuel System Check .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to Step 9

1. Check items that can cause an engine to run lean (Long Term FT significantly in the positive range) For a Lean condition.
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to Step 10

1. Spark plugs for proper heat range. Refer to General Information .
2. If incorrect spark plugs are installed, replace spark plugs as necessary.

Did any spark plugs require replacement?

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Go to Step 14.

Go to Step 11

1. Remove excessive carbon buildup with a top engine cleaner. Refer to instructions on top engine cleaner can.
2. Re-evaluate vehicle performance.

Is detonation still present?

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Go to Step 12

Go to Step 14

1. Check for an engine mechanical problem. Perform a cylinder compression check refer to Engine Mechanical .
2. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to Step 13

1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no malfunctions have been found, review/inspect the following:

•	Visual/physical inspection.

•	Scan Tool data.

•	Freeze Frame data/Failure Records Data.

•	All electrical connections within a suspected circuit and/or system.

3. If a problem is found, repair as necessary.

Was a problem found?

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Go to Step 14

Go to the Powertrain (OBD) System Check

Operate the vehicle to duplicate conditions present when the original symptom was noted.

Is symptom still present?

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Go to Step 3

Repair complete.