Info - Diagnostic Tips on Idle Speed Control (ISC) System for Engine Hesitation, Unstable Idling, Surge, Stall, P0510 and/or other DTCs, Poor Acceleration and/or Engine Speed Fluctuation Conditions
| Subject: | Diagnostic Tips on Idle Speed Control (ISC) System for Engine Hesitation, Unstable Idling, Poor Acceleration and/or Engine Speed Fluctuation Conditions |
| Models: | 2004-2005 Chevrolet Epica |
| with 2.5L Engine |
This bulletin is being issued to provide diagnostic information on the Idle Speed Control (ISC) system to reduce engine hesitation, unstable idling, poor acceleration and/or engine speed fluctuation conditions.
Dealers are requested to conduct a diagnosis of the ISC system and the related parts should a vehicle exhibit the above conditions. The following enhanced procedure has been developed to assist in diagnosing this condition. Most of the return warranty throttle bodies were found to be operating as designed.
Idle Speed Control (ISC) Schematic
Situation #1 - No Trouble Code(s) (DTCs) and No Reoccurrence of Condition
- Connect the scan tool.
- Start the engine.
- Run the engine until the coolant temperature reaches 90°C (194°F).
- Check for a throttle position (TP) sensor signal.
- If an abnormal TP sensor signal is found, test if the condition reappears after disconnecting/connecting the throttle body connectors.
- If the condition reappears, replace the throttle body.
- If an abnormal TP sensor signal is not found, the ISC system is OK and further diagnosis will be needed.
Situation #2 - Trouble Code(s) (DTCs) Stored
DTC | DTC Description | Recommended Field Correction |
|---|---|---|
P0122 | Throttle Position (TP) Sensor Low Voltage | Perform the Situation #1 procedure above. In case of no trouble found, Inspect the wiring harness or connector for a short circuit or poor connection. Then repair the condition. |
P0123 | Throttle Position (TP) Sensor High Voltage | |
P0222 | Idle Speed Control (ISC) Motor Position Sensor Circuit Low Voltage | |
P0223 | Idle Speed Control (ISC) Motor Position Sensor Circuit High Voltage | |
P0510 | Idle Position Switch Circuit | Clean the carbon deposit on the throttle body bore with cleaner and initiate the ISC learned values using a scan tool. If the same DTC reappears, replace the throttle body. |
P1511 *(P2101) | Idle Speed Control (ISC) Motor Control Circuit | Perform the Situation #1 procedure above. In case of no trouble found, inspect the wiring harness or connector for a short circuit or poor connection. Then repair the condition. |
P1512 *(P2118) | Idle Speed Control (ISC) System | Clean the carbon deposit in the throttle body bore with cleaner and initiate the ISC learned values using a scan tool. |
P1513 *(P2119) | Idle Speed Control (ISC) System Performance |
*( ) = 2005 Model Year DTC
Important: When the throttle valve is stuck due to carbon deposit, there will be a difference in actual position between the ISC driving motor and the return spring. There also will be a small movement within themselves to meet the target valve. In this case, the customer may feel a chattering sensation in the accelerator pedal and may find the engine speed fluctuating minutely. This is not a fault. If carbon deposit on the throttle valve and throttle bore is removed with a cleaner or the deposit by itself is gone, this symptom will disappear.
Parts Information
Part Number | Description |
|---|---|
96447970 | Body, Throttle |
Warranty Information
For vehicles repaired under warranty, use:
Labor Operation | Description | Labor Time |
|---|---|---|
J5490 | Body Unit, Throttle - Replace | Use Published Labor Operation Time |
Add | Diagnostic Time | 0.0-0.3 hr |
