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

Did you perform the On-Board Diagnostic (OBD) System Check?

--

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 present, correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

--

Go to Step 14

Go to Step 3

Did you perform a visual/physical check?

--

Go to Step 4

Go to Symptoms for the Visual /Physical Check

If the scan tool readings are normal, refer to Engine Scan Tool Data List , and there are no engine mechanical faults, fill the fuel tank with a known quality gasoline that has a minimum octane rating of 91 and re-evaluate the vehicle performance.

Is a detonation present?

--

Go to Step 5

Go to Step 14

1. Check the Transmission Range switch circuits. Use a scan tool, ensuring that the scan tool indicates that the vehicle is in Drive with the gear selector in Drive or Overdrive.
2. If a problem is present, diagnose and repair the Transmission Range switch as necessary. Refer to Transmission Diagnosis .

Was a problem found?

--

Go to Step 14

Go to Step 6

1. Check the TCC operation. Refer to Transmission Diagnosis .
2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 14

Go to Step 7

1. Check for any obvious overheating problems:

•	Low engine coolant

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

•	Inoperative electric cooling fans

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

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

Was a problem found?

--

Go to Step 14

Go to Step 8

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

Was a problem found?

--

Go to Step 14

Go to Step 9

1. Check the items that can cause the engine to run lean (Long Term Fuel Trim significantly in the positive range).
2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 14

Go to Step 10

1. Check the spark plugs for the proper heat range. Refer to General Information.
2. Replace any incorrect spark plugs that may have been installed, if necessary.

Did any spark plugs require a replacement?

--

Go to Step 14.

Go to Step 11

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

Is a detonation still present?

--

Go to Step 12

Go to Step 14

1. Check for the following Engine Mechanical problems (Refer to Engine Mechanical ):

•	Low compression

•	Sticking valves

•	A hydraulic valve lifter problem

•	Leaking cylinder head gaskets

•	A worn or incorrect camshaft

•	Incorrect cam timing

•	A damaged timing belt

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

Was a problem found?

--

Go to Step 14

Go to Step 13

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

•	The scan tool data

•	The Freeze Frame data

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

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

Was a problem found?

--

Go to Step 14

Go to Step 3

Operate the vehicle under the same conditions (as closely as possible) as when the original symptom occurred.

Is the original symptom still present?

--

Go to Step 3

The repair is complete. If another driveability symptom exists, refer to Symptoms .