First Problem With My '03

Tonight as I pulled up the driveway and stopped while the garage door was opening I get a delightful chime and a message center notice. "Reduced Engine Power". The check engine light came on and the Av immediately began idling VERY rough.

I pushed my OnStar button and had them run diagnostics. I've set a code P1516. She said it's a PCM failure and the vehicle needs service immediately.

Well, I did the logical thing. Shut it off completely and re-started it. Same thing. "Reduced Engine Power"

Shut if off waited 30 seconds. No warning, still had a Check Engine light but was running normally. Took it for a drive, runs fine. After the 5th Key Start the Check Engine light is gone too.

I know the old ECM's took 50 Keystarts to clear a code, not sure about the new ones.

Can someone give me more details on a code P1516 please.

SJP

SJProwler said:

Can someone give me more details on a code P1516 please.

Click to expand...

This is from the 2002 service manual. I assume it is the same for 2003, but I can't be 100% sure.


DTC P1516

Circuit Description

The predicted throttle position (TP), based on accelerator pedal position (APP) and other limiting factors, is compared to the Actual throttle position. The two values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the thottle actuator control (TAC) module redundantly monitor the predicted and actual throttle position. This DTC sets if the PCM detects an out of range condition between the predicted and actual throttle position.

Condition for Running the DTC

• DTC P1518 is not set.
• The ignition switch is in the crank or run position.
• The ignition voltage is greater than 5.23 volts.
• The TAC system is not in the battery saver mode.

Conditions for Setting the DTC

• The TAC module detects that the predicted and actual throttle positions are not within a calibrated range of each other or the PCM and TAC cannot determine throttle position or both TP sensors are invalid.
• All of the above conditions met for less then 1 second.

Action Taken When the DTC Sets

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
• The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
• The control module commands the TAC system to operate in the Reduced Engine Power mode
  OR
• Under certain circumstances the control module commands the engine OFF.
• The message center displays Reduced Engine Power.

Conditions for Clearing the MIL/DTC

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles. If no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and DTC with a scan tool.

Diagnostic Aids

• Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit of component conditions found during diagnostic testing.
• Verify that the starting and charging systems are working properly. Low system voltage can cause this DTC to set.
• When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on the system. Locating and repairing an individual condition may correct more than 1 DTC. Disconnecting components during testing my set additional DTCs. Remember this if you review the stored information in Capture Info.
• For an intermittant, refer to Intermittant Conditions on page 6-1217

It then goes on for two pages of a diagnostic flow chart. That's too much typing, sorry.

Hope this helps. It sounds like just what you described.

-- SS

Thanks -- SS

Somehow I knew you'd be the first one to answer me!

I guess if it does it again I'll go see the dealer, may have just been a freak thing.

SJP-=

I just had the reduced power mode light come on in my 02 last night . I did not know onstar could give you codes so I just limped it home .
I am wondering if the drl always on mod may have set the code . I have 11,600 miles with only an oil consumption and squeke & rattle problems so far (those are going in monday for repair) . However that was the first time I drove at night since I did the light mod (did it in the fuse block moved the 2 blue wires).
I am wondering if you may have done the same thing ? I will have the codes checked on monday when it goes in . But I am wondering if you did that mod & did it that way?