Accelerator Potentiometers
 

Replacing the broken rear trunk cable looked to be more than I might be able to manage, so I took my 2000 Boxster S in to Advanced European in Kenmore. They fixed the cable, but as I drove away, the CEL came on.

I went back the next day, they pulled the codes (1219 and 1577) and said those indicate the two potentiometers that are part of the electronic acceleration assembly are not sending the same signal. The mechanics are quite perplexed by two things:

1. They don't see what they could have done during the cable replacement to cause this (and maybe it is a really remarkable coincidence, though the car has never had the CEL come on before during it's 30K life).

2. Ordinarily when those codes come up, the computer puts the car into what they call "limp mode" where it will barely move. That's to protect against runaway acceleration from a faulty potentiometer. But the car continues to run fine.

They cleared the codes, but the CEL comes back on in a few minutes. I have an appointment Monday for them to check it out further, but I'm hoping someone here has some ideas about what's going on here.

Both components are part of the gas pedal sensor (PN#996.606.115.00). In addition to P codes, there are separate DTC (diagnostic trouble codes) and are either:

P1219

• 256 Accelerator pedal – Signal Implausible
  Potentiometer 1 or 2 outside the operating range.
  Potentiometer 1 to potentiometer 2 implausible.

P1577

• 427 Accelerator Pedal Potentiometer 1 – Signal Implausible
  Accelerator Pedal Potentiometer 1 – Below Limit
  Accelerator Pedal Potentiometer 1 – Above Limit

To isolate which problem is present, this needs to be checked with a DMM (or PST2 or PIWIS testers). Both potentiometers operate on a separate 5V power supply from the DME control module. Potentiometer 2 has a series resistor the size of the bulk resistance, so that its value only has half the inclination of potentiometer 1.

Unfortunately, if found faulty, the remedy is to replace the gas pedal sensor - $300+.

But, there may be another issue.
They would have likely disconnected the battery before working with the trunk cable lever due to the side impact airbag sensor being located in the same area. If so, when reconnecting, if they didn't have the key out of the ignition (or in position 1 or 2), they may have generated a fault code resulting in the CEL. The thing to try is disconnecting the battery for 5 or more minutes, then reconnect battery, switch on the ignition, wait one minute, Do Not press the accelerator, and finally switch off the ignition for at least 10 seconds. Then restart the car and re-check for faults. You can also check to be certain that no debris or such is obstructing the gas pedal .

If the Gods of Uusikaupunki are smiling on you, this may clear the code.

Thanks, Lil Bastard. Is the procedure you've suggested still a possible fix if, after the CEL occurred, they cleared the code and it re-occurred? I gather if the procedure were to fix the problem it would clear the current CEL, yes?

As always, I appreciate the help.

- Jim

Truly your guess is as good as mine. It's simple, and it couldn't hurt. But it just may save you a $300+ repair bill. Good luck!

Take the unit apart and clean with contact cleaner. I ran across this problem a few times over the years and always found the problem in the throttle body pot. But try the adaption procedure first.

I thought the battery/ignition procedure might have worked. I gave it a try and took it for a 3-mile drive with no CEL. Before it had come on within a mile or so. But the next drive a few minutes later brought it on again. It was certainly worth a try, though. Thanks for the info - maybe it will at least be a clue to the mechanics.

- Jim