I've been experiencing some problems with my car lately. As I'm going down the highway, the car suddenly goes into "limp mode". As I understand it, this is a mode that will protect your engine as you try to "limp" back to the fix-it shop.
During this mode, everything works, but the car is clearly not allowing itself to be pushed. The gas pedal, which used to work in a short range, has to be pushed almost to the floor to maintain speed.
The errors that I picked up on the OBD II reader are as follows:

P2135 TPS/Pedal Position Sensor/Switch A/B Voltage Correlation

P0121 TPS/Pedal Position Sensor A Ckt Range/Perf

P0222 TPS/Pedal Position Sensor/Switch B Circuit Low Input

I'm speculating, but here it goes: The errors tell me that the drive by wire probably uses two redundant circuits to sense input from the gas pedal (for safety reasons.) If the circuits do not correlate, then it goes into limp mode. Am I correct? If not, and you have a theory, I'm all ears.

Does anyone have a wiring diagram of the circuits? Because this typically happens when I hit a big bump, I'm wondering if a module might be loose somewhere in the car.

Thanks for any help.

Dave

 

maybe alldata.com can help....they usual have a diagnostic tree to follow for codes or a tester like snapon...sounds like the pedal assembly but i would not want to buy one until i knew for sure. it wont be cheap...good luck let us know

 

Try disconnecting your battery for a few minutes and letting the throttle body re-adapt. That sometimes corrects throttle position sensor issues. It's not always that simple, but it's an easy thing to try before you dig any deeper.

 

Thanks for the feedback.

Anyone know where the sensors are for the drive by wire? Are they specific modules near the engine? I'd like to see if one or both are partially unplugged.

Dave

 

for what its worth....a corvette has 3 tps [all in one unit] on the gas pedal assembly which gives your command to the TAC module which sends commands to the throttle body acuator controller. is your throttle body stock ?

 

Ex,
Yes, the throttle body is stock. If both sensors are in that black box under the gas pedal, then I'll check to see if there is anything loose. I couldn't imagine that a throttle could go bad. I would imagine that they need to be bullet proof.

Tom,
I unplugged the battery for a few minutes. After restart, and of course, entering the stereo code in, the car ran like a beast!!! I'm not sure what was reset in the ECU, but it definitely cleared out some cobwebs in there.

I'll monitor the throttle in the coming days to see if there is any reoccurrence.

Thanks for the input.

Dave

 

Crap. It came back today.

 

Alright. I've looked through around 200 pages of wiring diagrams. I can't find anything that speaks to e-gas or electronic throttle. I did, however, find a white paper on the Boxster:

"The Motronic ME 7.2 engine control unit, which Porsche added in model-year 2000, essentially duplicates the functions of the ME 5.2 unit, but with the significant addition of the E-Gas electronic throttle control. Instead of the gas pedal pulling a cable attached to the throttle valve, it pulls a short cable connected to a pedal value transmitter in the dashboard. The transmitter uses a potentiometer to convert the pedal travel path and speed into an electronic signal.
The control module processes the signal, sending it to an electric motor that operates the throttle valve. By providing full computer control over air intake at all engine speeds, the electronic throttle control enhances throttle response and helps reduce emissions. The system also reduces parts, since it eliminates the throttle linkage and separate idle speed control."

The question I have is whether the pedal position sensors are both on the motor that controls the throttle body? Anyone familiar with these?

I could just take it to the dealer, but I'm having fun figuring these things out.

Dave

 

Hey Dave, did you ever figure out this problem...mine is doing the same thing and battery reset didnt work...

 

I'm short of time and my e-Gas reference is not handy anyway, but the e-Gas system does have two potentiometers which provide a redundancy and self check.

If there is any disagreement the system defaults to limp mode and one or more error codes are stored.

The potentiometers are in the pedal.

What you might try is to carefully remove the pedal assembly and check for dirt or whatever. My 02 Boxster gas pedal as been in service now for over 262K miles and I've never had to touch it but a few owners have reported having some success cleaning the thing. I have not had the one in my car out so I do not know what's involved. Also, it might not be the cleaning that helps but the disconnecting the thing from the harness then reconnecting it. This re-establishes a better electrical connection.

 

I would think more along the lines of the throttle position sensor on the throttle body itself. It may be part of the throttle body and not serviceable on its own, with the drive by wire system.

Mike.

 

The error codes the OP posted point to the throttle position sensors in the pedal.

There are separate error codes for the TB.