TPS, Throttle Body, & Pedal Codes

[cheetah]

Hello.

2002 Boxster S 6-speed

I suddenly am having a problem: When the vehicle is on, the accelerator pedal does not do anything (no affect on the engine at all). I know that I have the throttle-by-wire, but here is a quick background of what I have done recently…

I changed the clutch (not really a bad job at all surprisingly) and all of the sudden I am having the pedal problem. I had cleaned the throttle body while the clutch was being done, but everything seems to be in order there (took the electronics apart and all seems to look perfect). It ran fine after the clutch job for a few days.

I have the Durametric, and it comes up with the following codes:

P1219 – Porsche Code 256 – Accelerator Pedal Potentiometer
P1578 – Porsche Code 428 – Accelerator Pedal Potentiometer
P0121 – Porsche Code 117 – Throttle Valve
P1121 – Porsche Code 430 – Throttle Position Sensor
P1122 – Porsche Code 431 – Throttle Position Sensor
P0103 – Porsche Code 115 – Mass Air Flow Sensor

So I ran a real-time watch of the sensor values, and came up with the following:

Mass air flow: 48.5 kg/h
Pedal value: 30.07%
Pedal encoder potentiometer 1: 4.54V
Pedal encoder potentiometer 2: 4.54V
Setpoint throttle: 2.98%
Actual value throttle: 116.8%
Throttle position sensor: 5.00V
Throttle position sensor: 5.00V
Throttle plate angle potentiometer 1: 116.8%
Throttle plate angle potentiometer 2: -14.1%
Mass air flow sensor: 4.99V


I have tried the “normal” fixes: car on accessory for 1 minute, then off for 10 sec, and disconnecting the MAF. Disconnecting the MAF made the car run worse, so it should be fine. I also disconnected the battery for a bit to no avail.

Can this be a problem with the pedal assembly? I see the 5V readings on the TPS, is that a broken ground or something like that? It sounds like a maximum value? The throttle body is properly plugged in, and the plug shows no sign of damage. How is this wire loomed to the pedal and computer? It disappears under the intake manifold.

Any tips would be greatly appreciated. I have only had the car for a few months, but I have put a lot into it, and I want to drive it for the final few weeks of nice weather here, and this is frustrating. 

BTW, photos of the car can be seen at:

http://www.myspace.com/cheetahonline

http://www.cheetahonline.com/vehicles/boxster.html


Thanks,
Paul

[spine911]

Originally Posted by cheetah

Hello.

2002 Boxster S 6-speed

I suddenly am having a problem: When the vehicle is on, the accelerator pedal does not do anything (no affect on the engine at all).

Can you further explain this statement? Im assuming you can start the car normally, can you be more descriptive on what happens when you depress on the pedal??? Does the engine rev up, Can you shift when the engine is on?, etc...pls. be more descriptive.

[cheetah]

The car starts normally, but pressing the accelerator pedal does not rev up the engine at all. I have not tried to shift, as the car is in the garage.

[tholyoak]

You have appear to have a major wiring issue. All your values are maxed out at 5V. Some of these faults cause a limit to the pedal value at 30%. The throttle body values indicate the TB is fully open.

The diagnostic for these faults is to first check the wiring since it is unlikely that the throttle potentiometer and the throttle body and the MAF are defective simultaneously. If the wiring is OK then the other possible cause is a bad DME.

Todd

Originally Posted by cheetah

Hello.

2002 Boxster S 6-speed

I suddenly am having a problem: When the vehicle is on, the accelerator pedal does not do anything (no affect on the engine at all). I know that I have the throttle-by-wire, but here is a quick background of what I have done recently…

I changed the clutch (not really a bad job at all surprisingly) and all of the sudden I am having the pedal problem. I had cleaned the throttle body while the clutch was being done, but everything seems to be in order there (took the electronics apart and all seems to look perfect). It ran fine after the clutch job for a few days.

I have the Durametric, and it comes up with the following codes:

P1219 – Porsche Code 256 – Accelerator Pedal Potentiometer
P1578 – Porsche Code 428 – Accelerator Pedal Potentiometer
P0121 – Porsche Code 117 – Throttle Valve
P1121 – Porsche Code 430 – Throttle Position Sensor
P1122 – Porsche Code 431 – Throttle Position Sensor
P0103 – Porsche Code 115 – Mass Air Flow Sensor

So I ran a real-time watch of the sensor values, and came up with the following:

Mass air flow: 48.5 kg/h
Pedal value: 30.07%
Pedal encoder potentiometer 1: 4.54V
Pedal encoder potentiometer 2: 4.54V
Setpoint throttle: 2.98%
Actual value throttle: 116.8%
Throttle position sensor: 5.00V
Throttle position sensor: 5.00V
Throttle plate angle potentiometer 1: 116.8%
Throttle plate angle potentiometer 2: -14.1%
Mass air flow sensor: 4.99V


I have tried the “normal” fixes: car on accessory for 1 minute, then off for 10 sec, and disconnecting the MAF. Disconnecting the MAF made the car run worse, so it should be fine. I also disconnected the battery for a bit to no avail.

Can this be a problem with the pedal assembly? I see the 5V readings on the TPS, is that a broken ground or something like that? It sounds like a maximum value? The throttle body is properly plugged in, and the plug shows no sign of damage. How is this wire loomed to the pedal and computer? It disappears under the intake manifold.

Any tips would be greatly appreciated. I have only had the car for a few months, but I have put a lot into it, and I want to drive it for the final few weeks of nice weather here, and this is frustrating. 

BTW, photos of the car can be seen at:

http://www.myspace.com/cheetahonline

http://www.cheetahonline.com/vehicles/boxster.html


Thanks,
Paul

[cheetah]

For future reference, this was a problem with the MAF sensors ground (which goes to the ECM at Pin C9). Once this ground was re-established, all is well.

This job would have not been possible without my Bentley book and Durametric tool. This are a must for anyone who doesn't or can't take the car to the dealer for everything...

Thanks to everyone who replied,
Paul

[djomlas]

sweet, i was looking at this thread like wow, what is happening to that car?

im glad it all worked out man, and didn't cost you anything. gotta love the satisfaction

[cheetah]

I know, I was getting frustrated. I had it down for a bit doing the clutch, etc., then I was out in LA, then TX, and came home and wanted to drive my car!

I did quite a bit else while the car was down, so it runs wonderfully now. I put on Deluboz headers, fixed a strut tower top bolt, put on the rear STB, rebuilt both axles with new boots, new solid front motor mount, along with the clutch kit.

So the car finally drives the way that it should. Buying used, there are always some things that need fixed, but the car is now the way that it should be.

I LOVE the fact that I was able to figure it out. While I couldn't have done it without the book and Durametric; with them a person in their garage can save a lot of money and trips to the dealer. For me, the closest dealer is 40 miles away, so I don't plan on ever going there, except to turn on my OBC hack! hehe (already installed, just waiting to turn in on)