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 Engine Scan Tool Data List . If 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 the Transmission pressure switch manifold. Refer to 4L60-E Automatic Transmission 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 6

1. Check TCC operation. Refer to 4L60-E Automatic Transmission 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. Refer to Cooling System Diagnosis in Radiator and Cooling.

•	Restricted water flow through radiator. Refer to Cooling System Diagnosis in Radiator and Cooling.

•	Restricted air flow to radiator. Refer to Cooling System Diagnosis in Radiator and Cooling.

•	Inoperative electric cooling fan circuit(s) Refer to Electric Cooling Fan Diagnosis refer to .

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

•	EGR operation. Refer to DTC P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient .

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 the engine to run lean (long term fuel trim significantly in the positive range). Refer to DTC P0171 Fuel Trim System Lean Bank 1 .
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.

Was a problem found?

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Go to Step 14

Go to Step 11

1. Remove excessive carbon buildup with top engine cleaner. Refer to instructions included with the top engine cleaner.
2. Re-evaluate vehicle performance.

Is detonation still present?

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Go to Step 12

Go to Step 14

1. Perform a cylinder compression check. Refer to Engine Compression Test in Engine General Information and Mechanical 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 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. Refer to Visual/Physical Checks .

•	Scan tool data. Refer to Engine Scan Tool Data List .

•	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

Review technical 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