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 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

Perform the careful visual/physical checks as described at the start of Symptoms section.

Was the visual/physical check performed?

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Go to Step 4

Go to Important Preliminary Checks

If the scan tool readings are normal, Refer to Engine Scan Tool Data List and there are no engine mechanical malfunction, fill fuel tank with a known quality gasoline that has a minimum octane reading of 92 and re-evaluate vehicle performance.

Is the detonation present?

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Go to Step 5

Go to Step 14

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.

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 the fuel pressure. Refer to Fuel System 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 the items that can cause an engine to run lean. For a lean condition, refer to DTC P0171 Fuel Trim System Lean for 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 8

1. Check the spark plugs for proper heat range. Refer to Ignition System 6D4 .
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 9

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

Is the detonation still present?

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Go to Step 10

Go to Step 14

1. Check the Knock Sensor (KS) system for proper operation. Refer to Knock Sensor (KS) System Diagnosis for 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 11

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 12

1. Check the intake valves for valve deposits.
2. If deposits are found, remove as necessary.

Were deposits found on the intake valves?

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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 items:

•	Visual/physical inspection.

•	Scan tool data.

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

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

Is the action complete?

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Go to Step 14

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Operate vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

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System OK

Go to Step 2