For 1990-2009 cars

# Cold Hesitation on Acceleration and a Possible P0171 DTC - keywords accelerate CEL hesitate MIL performance sag SES start temperature

Subject: | Cold Hesitation on Acceleration and a Possible P0171 DTC

Models: | 2000 - 2002 Chevrolet Prizm

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

### Condition/Concern:

On rare occasions, a hesitation may be experienced on acceleration before the engine reaches operating temperature. Additionally, a SES light with a P0171 DTC may or may not be present.

### Recommendation/Instructions:

If the SI diagnostics do not isolate the cause of this concern, perform the following suggestions as necessary:

• | Verify the MAF sensor grams per second at a hot idle while in park with all accessories off. Typically, this value should be between 2.2 to 2.6 grams per second at a hot idle while in park with all accessories off. If possible, compare the value to a known good vehicle at the same operating conditions to confirm MAF sensor accuracy. If necessary, replace the MAF sensor.

• | Decarbon the engine with two cans of top engine cleaner. Run the first can of cleaner through the engine by following the instructions on the can and let it soak for 2 hours or more. After soaking, drive the vehicle and repeat this a second time. After the decarboning is complete, it may be beneficial to change the engine oil and filter.

| Important: DO NOT force the engine to stall while inducing the top engine cleaner.

• | Pump the gas tank out and refill with quality 87-octane gasoline. If this eliminates the concern, advise the customer to use only 87-octane gasoline from a high quality, high volume filling station, such as those described in top tier fuel bulletin 04-06-04-047.

Note: If all of the steps above are performed without success but an obvious improvement was noted after decarboning the engine, this may be due to valve deposits. If this is related to valve deposits and decarboning does not eliminate the concern, it will be necessary to remove the cylinder head and manually clean the valves.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.