Contour Enthusiasts Group Archives Forums General Troubleshooting idle speed control circuit open (p1508)

hello there...
my friendly little CEL has just notified me of the above problem with my car...and im trying to figure out what i can do to fix it/if it even needs fixing/what the consequences are.

as far as i can tell, there hasnt been any change in performance or fuel economy in the car since the light went on. i have the chilton repair manual, and according to them, such a code doesnt even exist. basically what im wondering is what it means that the idle speed control circuit is "open". does that mean i need to replace the air control valve?

1998 contour sport
2.5L DOHC V6
Automatic Tranny

any help you guys could give me is much appreciated.

peace
-tk

im pretty sure its PO508... But that still doesnt make sense. The lowest 500 code is 511, and thats the PCM memory.. Maybe, reset your computer and see if the code comes back... Then read it again and see what it might REALLY be.

The IAC circuit is set up so that one side of the solenoid coil is connected to battery power (via fuses, etc). The other side of the coil is then "grounded" under the control of a transistor-like switching device inside of the PCM. This driver has an auxillary sense circuit so that the PCM can check to make certain that the drive signal was applied to the solenoid when commanded to do so and that the signal was as expected..

If the sensing circuit fails to see either the battery voltage or fails to see a change in voltage when it should have, it assumes that the circuit is open (i.e., open connector, IAC, coil, wiring, etc).

Since you report no issues with driveability or idling, I would assume that the IAC circuit is functional and that the fault is internal to the PCM in the self-monitoring circuitry.

Other than checking to make sure the IAC connector is not loose, I would recommend only getting the exact code and consulting the troubleshooting instructions contained in the PCED before doing anything else. Proper diagnsis would require a scan tool to monitor the IAC PIDs.

Steve

Steve

ALIAS: its most def 1508...i checked code out online, and apparently its a valid code.

projectsho89: thanks...since it looks like its not hurting anything, i suppose ill let it go until summer when i fix all the other little things that need fixin...unless of course you can think of any problems it may cause in the long run.

thanks

-tk