Engine Controls - Intermittent Lack of Power
BULLETIN NO.: 99-T-34ISSUE DATE: August, 1999
GROUP/SEQ. NO.: Engine-09
CORPORATION NO.: 99-06-04-027
SUBJECT:
Intermittent Lack Of Power
(Replace Knock Sensor - P/N 10456222)
MODELS AFFECTED:
1996 - 1997 Saturn S-Series vehicles equipped with DOHC (LLO) engines
CONDITION:
Some customers may comment about an intermittent lack of power on acceleration on vehicles equipped with DOHC (LLO) engines.
CAUSE:
This condition can be caused by the powertrain control module (PCM) unnecessarily retarding spark timing as a result of normal engine noises (not spark knock) being detected by the knock sensor.
The knock sensor used in DOHC engines is "tuned" to a specific frequency associated with spark knock. Production variation in engine manufacturing may result in slight differences between normal engine noise frequencies. The frequency range of production knock sensors may not account for normal engine noises and may incorrectly cause the PCM to retard spark timing which leads to an intermittent lack of power.
CORRECTION:
1. Evaluate vehicle under operating conditions described by customer.
2. Using a Scan tool, monitor the following parameters in the Spark Control screen under the Engine Data Display.
^ LOW SPARK MODIFIER
^ MID SPARK MODIFIER
^ HIGH SPARK MODIFIER
3. Determine if ALL three of the following conditions apply:
^ No audible spark knock is present.
^ Knock Sensor Counts (in degrees) occur mostly in the HIGH SPARK MODIFIER.
^ HIGH SPARK MODIFIER is greater than 9.00.
If ALL of the above listed conditions apply, replace knock sensor (P/N 10456222). (Refer to "Knock Sensor" removal and installation procedures in the Ignition/Spark Control section of the appropriate model year Powertrain Controls service manual.)
If the LOW, MID, and HIGH spark modifiers are all at or near the maximum value of 9.80, installing new knock sensor (P/N 10456222) will not resolve the lack of power condition. If this is the case or any of the above listed conditions do not apply, refer to additional diagnostic information (Low Power, Spark Knock, or DTC P0326) in the appropriate model year Powertrain Controls service manual.
PARTS REQUIREMENTS:
10456222 Sensor Asm - Knock
CLAIM INFORMATION:
To receive credit for this repair during the warranty coverage period, submit a claim through the Saturn Dealer System as shown.