2003 Boxster S 3.2 No Run / No Start: P0121/P1121/P1122

[pallen747]

Hi all, Need some tech help.
I am using Autel OBDI unit. Have the below codes and read outs. I have replaced the Throttle body - no change.
P0121 says Accel pedal potentiometer.
P1121 says Throttle position sensor 1.
P1122 says Throttle potentiometer 2.
From what I have read it could be the throttle pedal potentiometer failed or DME failed?? Possibly earth to DME from MAF??
One is a PITA but cheap to replace - the other, well extremely expensive the MAF is just a guess.
Anyone else had similar? Any advice?
Thanks.

[blue62]

Originally Posted by pallen747

Hi all, Need some tech help.
I am using Autel OBDI unit. Have the below codes and read outs. I have replaced the Throttle body - no change.
P0121 says Accel pedal potentiometer.
P1121 says Throttle position sensor 1.
P1122 says Throttle potentiometer 2.
From what I have read it could be the throttle pedal potentiometer failed or DME failed?? Possibly earth to DME from MAF??
One is a PITA but cheap to replace - the other, well extremely expensive the MAF is just a guess.
Anyone else had similar? Any advice?
Thanks.

Have you tried to re calibrate the throttle?
Disconnect the battery for a few minutes to reset the DME/ECU
Then turn key to on position for 1 minute do not start.
turn key of for 30 seconds.
then see if car starts.

The P1121 code is for the heater circuit on bank 2 post cat O2 sensor.
You have to be careful when looking up P-codes for these cars as they changed on some year models.
Usually when the DME/ECU was upgraded.

I see that it will not even start.
Sounds like you may have some wiring issues.

Can you give some background on the car?
Did it run in the past?
Was work done on the car before the no start issue?
Are there any mods to the car?
Has water gotten inside and under the drivers seat?

[pallen747]

Thanks Blue62.
I tried the reset function, but I will try it again. The car has been running but just at idle. has been static for 3 years outside (in Iceland but UK car). The problems started then. Basically the owner had zero throttle response. He was told it was the Throttle body, which he replaced. Now it wont start. I came onto the project late as he needs held. As mentioned I am using a new Autel 808 obdi reader with latest updates, so I was assuming code read outs would be correct. Having said that even with a post Cat O2 sensor inop it should still start/run. May I ask where I can find the correct codes for an 03 Boxster S?
The Throttle body is the only work that I am aware of. No Mods.
I will check under the drivers seat for dampness. Is that where the ECU lives?
Thanks Paul.

[blue62]

Originally Posted by pallen747

Thanks Blue62.
I tried the reset function, but I will try it again. The car has been running but just at idle. has been static for 3 years outside (in Iceland but UK car). The problems started then. Basically the owner had zero throttle response. He was told it was the Throttle body, which he replaced. Now it wont start. I came onto the project late as he needs held. As mentioned I am using a new Autel 808 obdi reader with latest updates, so I was assuming code read outs would be correct. Having said that even with a post Cat O2 sensor inop it should still start/run. May I ask where I can find the correct codes for an 03 Boxster S?
The Throttle body is the only work that I am aware of. No Mods.
I will check under the drivers seat for dampness. Is that where the ECU lives?
Thanks Paul.

First: your code reader is reading correctly. Its when you look up the code.
you have to make sure your looking at the proper DME/ECU series.
For A 5.2 series DME/ECU the P-1121 code is for the throttle issue.
For a 7.2 series DME/ECU the same P-1121 code is for the O2 sensor so you have to be careful.
You have a 2003 year model so you will have the 7.2 series or maybe even the 7.8 series DME/ECU.
Second:
I look up codes in the Bentley Service Manual then also try to cross check them online.
Because the Bentley is not always correct.

Third:
The immobilizer is under the drivers seat (left hand in US) they are very susceptible to moisture.
If it is the issue it will cut all spark and fuel to the engine.

Fourth:
If it is not starting or not even firing the first thing to do is see if you are getting spark.
then test for fuel.
you can listen for the fuel pump to run when you turn the key on.
But a better way is to test fuel pressure at the fuel rail in the engine bay.
There is a presta valve on the fuel rail that you can attach a fuel pressure gauge to.
If you not getting fuel or spark then the immobilizer is most likely the issue.
Hope this helps
Let me know how you go

[pallen747]

Thanks Blue62.
Excellent info on the DME codes and dash number.
It is firing just not starting (I should have been much clearer).
When the guy has replaced the battery I will do the throttle reset (Turn key to on position for 1 minute do not start. Turn key of for 30 seconds - retry).
I will also check in the Autel for a read out of the throttle pedal potentiometers to make sure they are both operating and sending a correct signal to the DME.
I believe from my research that one signal should be approx double the value of the other? Is this correct?
Once I have done more trouble shooting I will get back to you.
Thank you so much for your time and advice - very much appreciated.
Paul.

[blue62]

Originally Posted by pallen747

Thanks Blue62.
Excellent info on the DME codes and dash number.
It is firing just not starting (I should have been much clearer).
When the guy has replaced the battery I will do the throttle reset (Turn key to on position for 1 minute do not start. Turn key of for 30 seconds - retry).
I will also check in the Autel for a read out of the throttle pedal potentiometers to make sure they are both operating and sending a correct signal to the DME.
I believe from my research that one signal should be approx double the value of the other? Is this correct?
Once I have done more trouble shooting I will get back to you.
Thank you so much for your time and advice - very much appreciated.
Paul.

On the potentometer signals I think you are correct.
You can use the search function here on the forum and find old threads.
type in E-gas in the search at the top of the page.
Should be some threads on how e-gas works.

If the car fires you should be able to get it running sooner or later.
Even if the E-gas is faulty the car should start although it would probably default to limp mode.

I would do a fuel pressure test at the fuel rail.
Your getting spark so it seems like a fuel issue.
If you need specs. and testing procedure try the search function.
or let me know and I will see what I can find in the service manual.
keep me posted I will try to help with diagnosis.

[pallen747]

You're a good man, thanks.

[blue62]

Originally Posted by pallen747

You're a good man, thanks.

I should have mentioned this before.
Perhaps you have already done it.
But any good diagnostic procedures starts with the basics.
So you should make sure all the fuses and relays are good.
Especially those for fuel pump, fuel injectors, and the DME/ECU.
Also that the battery is good.

[thom4782]

What about a bad crank position sensor...car would turn over, but not start

[blue62]

Originally Posted by thom4782

What about a bad crank position sensor...car would turn over, but not start

OP states engine fires. just doesn't start.
Could be a bad crank position sensor.
But I try to go with basic diagnostic procedures.
That means go from the simplest to the most complex.
Step by step.
So Fuses, relays, battery.
Air, Spark, Fuel.
Those are the most basic.
He is getting spark.
need to see if he is getting correct fuel pressure.
OP also has codes related to the E-gas so throttle position sensor could be an issue.
If fuel pressure proves good.
Then I would go up the ladder to things like throttle position sensor, crank position sensor, step by step.

[blue62]

Pallen747
I sent you a PM let me know if you got it and if it works.
It is a link to a diagnostic tech manual for the 7.8 DME/ECU.
I believe the car your working on is running that DME/ECU series.
It has all the OBDII codes and how to diagnose all those codes.

[Stl-986]

03 is going to be 7.8

have you cleared the codes and then see if they come back?
Made sure the TB wiring is connected (this gets missed many times when working on the car)

Does the tach bounce when trying to start?
pushing the throttle down when trying to start does it do anything different?

sitting this long at a minimum I would drain all the gas and put in 5 gal of new gas along with a bottle of HEAT.

I worked on a car for 3 days...would crank but never fire. Let fuel out of the fuel rail and it was white. Drained the tank, put in new gas and it fired right up.