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 On Board Diagnostic (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 Checks

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 87 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 circuit; 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 4T60-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 4T60-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). Refer to Electric Cooling Fan Diagnosis.

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

•	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 Pressure Test .
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 fuel trim significantly in the positive range). Refer to DTC P0171 Fuel Trim System Lean .
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. Check 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 section).
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

Refer to Technical Service Bulletins

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

System OK