I've been having some issues with throttle response on my 2008 CTT, resulting in significantly reduced power delivery and a CEL that reappears. CEL appears: "P0220 - Throttle/Pedal Position Sensor Switch 'B' Circuit Low".

Throttle body, including throttle body sensor, has been replaced with OEM as of last week. I have a new pedal assembly on the way, and will swap that out when it arrives this week. I checked the throttle wiring harness at ends (though not continuously) at the pedal and the throttle body, and those seem OK. I even disassembled and reassembled the pedal body to see how the sensor gets its input. Nothing looked amiss, but I'll still swap it out. There are two circuits, of course, and the pedal position simply informs the voltage on the circuits.

I logged both the throttle pot values and pedal encoder pot values (each a pair, that work in inverse), and got the following, indicating that the pedal potentiometer 2 starts at a reasonable voltage, then drops to 0 and never moves. The drop to 0 corresponds to pushing on the accelerator to bring the engine rpm above 1000 - at that point, the engine never returns to normal idle (~580rpm), but sits at 1000rpm almost exactly. This behavior is repeatable.

Question: What would cause the Pedal Encoder Potentiometer 2 to be reporting incorrectly, delivering the above CEL (I presume)?

Pot values:




Engine data (ambient, rpm, boost pressure). The impact of the throttle issue is, presumably, the throttle plate angle not being "correct" based on pedal travel (though, correct according to the read values), and no boost until much higher RPM than normal:

 

Values from the new pedal. We may be in business. I've yet to take it for a test drive.

After installing the new pedal and on first startup, the vehicle did an adaptation before settling back down to normal idle RPM. I'm optimistic:

 

Excessive mashing of the pedal to the floor was the cause LOL?

 

Hah - the most recent set of values with the new pedal was at idle and parked. Just testing the voltage.

"Pedal Encoder Potentiometer 2" was clearly borked.

 

Never mind - problem back, same as before.

I'm out of time to continue to diagnose, and will probably sell. It's probably a minor issue but work has me fully occupied and the nearest dealer/specialized indy is 2+ hours away.

 

You got my attention when you talked about selling for such a minor problem. Hope I can help here.

I am not familiar with this circuit, but it looks to me like a problem with the wiring for the pedal encoder potentiometer 2 (red line, call it PEP2). Guessing it should mirror PEP1, so PEP1 + PEP2 = 5V, which is what TP1 and TP2 seem to do (TP1 + TP2 = 5V).

With that line dead, or problematic, and using only PEP1, it might be acting as if you're pressing the pedal only half as far as you actually are. Sound right?

So I'd double check the connectors + wiring on both ends of that wire in the circuit. Make your own actual voltage measurements rather than relying on the ECU output (I assume that's where you got the plots) - see if they confirm the plots, to see where the signal is dropping out. Then maybe splice in a parallel test line to bypass the doubtful wire and see if things work again.

Do you have the wiring diagram?

Any other problems with the car that might be electrically related?

 

Thank you for the nudge. I went out after dinner and traced the wiring as best I could. I found a 955 wiring diagram for cruise control that indicates the pedal sensor going to the DME, and then I found the route that it takes through the firewall and to the DME. DME is out and I'm going to do some testing with a multimeter today.

What I'd really like to do is test the circuits all the way to the harness that plugs into the DME, but I can't find an accurate pinout for the 957 Turbo.

No other electrical gremlins, but I'm still going to test the battery voltage directly this morning.

I think your description of PEP1/PEP2 is spot on. It mirrors the behavior I'm seeing with pedal travel and throttle behavior.

 

So, I checked the battery voltage (directly at the battery), and got a 12.24v reading. My understanding is that 12.5v is really the minimum acceptable? With that in mind, I charged up the battery, and we're back to the races - no more P0222 code, performing as normal (or, slightly better, perhaps, with the new throttle body).

I do have a set of 2008CTT wiring diagrams (and 2009 as well). Happy to share individually for those who are in need. Cruise control diagram attached.

I'll dig into the wires soon to test the circuit.

 

Nice that you found the diagram. Looks very helpful. The data you've shown suggests the Pedal#2 signal is bad. Same results with a new pedal suggests a problem with the wiring (or unlikely the ECU).

Diagram looks complicated until you get to the part that actually matters - the pedal, very nicely showing everything. Looks to me like for redundancy (as they should have on a critical system like this) they have two copies of the same thing. A potentiometer (or equivalent) that takes in +5V and GND, the position of the pot produces a voltage measurement that is returned as the signal to the ECU - which probably compares + combines the two, etc. to trigger a fault code and control the throttle.




For pedal #1, which seems to work, and may be useful for comparison with the suspected bad pedal #2:
+5V comes in on 2-BLU/BRN at pedal (A53-BLU/YEL on ECU).
GND is 4-YEL/BLK at pedal (A39-YEL/BLK on ECU).
signal out is 3-YEL/GRN at pedal (A38-BRN/GRN on ECU).

For pedal #2, suspected bad:
+5V comes in on 1-GRN at pedal (A40-GRN on ECU).
GND is 5-BLU/RED at pedal (A51-BRN/BLU on ECU).
signal out is 6-BRN/GRY at pedal (A52-BLU/RED on ECU).

Note that signal and ground are asymmetric between pedals 1 and 2 - so that way, they nominally add to 5V, which may be part of their simplified fault detection (my guess).

Simple testing you could try:
disconnect connector at pedal,
- confirm +5V supplied at 1 and 2, vs. a grounding point in the car.
- confirm +5V between 1 (high) and 5 (low) = supply for pedal 1 <== should be good
- confirm +5V between 2 (high) and 4 (low) = supply for pedal 2 <== might be bad

If those are good, the pedal is getting the power and ground properly. Assuming the replacement part is good, it will be correctly producing the signals. So next guess is that they might not be getting back to the ECU correctly.

If you can access the connectors at the ECU (A38-40 and A51-53), disconnect and measure for continuity from that end of the wiring to the pedal connector.

pedal #1, working properly should show zero resistance on these pairs (and I'd do this as a test of the test):
2-BLU/BRN at pedal <==> A53-BLU/YEL on ECU
4-YEL/BLK at pedal <==> A39-YEL/BLK on ECU
3-YEL/GRN at pedal <==> A38-BRN/GRN on ECU

pedal #2 should show zero resistance on these pairs:
1-GRN at pedal <==> A40-GRN on ECU
5-BLU/RED at pedal <==> A51-BRN/BLU on ECU
6-BRN/GRY at pedal <==> A52-BLU/RED on ECU <== if the power + ground tests above were good, this is the one likely to be bad

 

Wow, thank you. I'll be tackling this again in the morning, and I'll follow your lead on the steps to take to troubleshoot, starting with the pedals. I suspect that the ECU isn't getting the signals.

I will follow up after this weekend's work. Thanks again.

 

No additional testing yet, but I did install a new, beefier battery this morning. The problem has not returned yet. We'll see what the testing brings.

 

I was able to check enough circuits with the multimeter to effectively rule out the wiring as the source of the problem. End-to-end, things looks OK there.

Based on your suggested pedal tests, oldskewel, I was able to confirm that the original (old) pedal and the new pedal are grounded. However, the old pedal wasn't delivering much voltage change (measured at the wire near the pedal, to rule out the problem being the signal line to ECU or ECU reading itself) on pedal sensor 2 when the pedal moved through travel. On closer inspection, the brush that moves along the +5V plate for sensor 2 is rough and appeared damaged. None of these symptoms are present for the new pedal. What's odd, though, is that even with the old pedal, there's initially a good signal on that sensor 2 +5V rail, until the pedal hits a certain point in the travel - then, the voltage drops to 0 and stays there. I presume this is due to the brush making adequate or full contact at the starting point, but not beyond.

My assertion is that the old pedal is indeed the problem, and my assumption is that the new pedal also displaying similar symptoms initially is because I didn't properly give the ECU time enough to adapt (there is an adaptation procedure, which is simple and just involves some waiting with key on but engine off). I adapted the throttle body, too, using my Durametric, since I'd replaced that as well, though the shop that replaced it said they did an adaptation. I suppose adapting the system again after subsequently replacing the pedal was needed anyway.

Thanks for the assist on this. At least I replaced a few items that needed attention anyway, and got a new battery as well. So, all's well that ends well (today, at least!).

 

My 05 CTT seems to have a similar problem, but to a lesser degree.
Its hard to notice while driving, but if I slowly rev the engine to around 1000-1200 rom and hold it there perfectly steady, it jumps down to issue them back up to the 1000-1200 rpm, at a frequency o about once every 2 seconds, as if its reading the throttle correctly, then not.
i was suspecting bad contacts on the throttle body, and plan to remove the black cap on the side and see if anything needs cleaning (i recall doing similar on old bmw and toyota bosch intake flap sensors). And to make sure the tracks/contacts look intact.
Sounds like the same is true for the pedal side, a potentiometer that could be messed up or needs cleaning.
i think its affecting throttle in the 3000-3300 range, another dead spot so to speak.
I have an icarscan and have reset throttle and trans adaptions, as well as the 60 second let the throttle adaption do its own thing, no change.
Ill see if I can read any anomolies with the icarscan and throttle voltage.