P0221

[Massa in Perth]

Hi all, hoping to get some help with this problem, and to collect some info for others to use.

I fitted an after market contactless Pedal Pot sensor (thanks Davy) a couple of months ago. previous original sensor had been hard wired but was not causing problems. Item was professionally fitted, used a new plug and followed the instructions I was sent with the sensor.

A month or so later I started getting P0221 ( Throttle/Pedal Position Sensor/Switch "B" Circuit Range/Performance).

The error code description is quoted as follows:
Possible causes of OBD code P0221
- Harness or connector (The TP sensor 1 circuit is open or shorted.) - Electric throttle control actuator (TP sensor 1) may be faulty The Error code is generally activated on detection of the following conditions: An unexpected voltage from the TP sensor 1 is sent to ECM.

Have been getting increasingly common and persistent CELs, always P0221, accompanied by limp home mode.

Davy and I have been working through a number of steps .He has been brilliant throughout and I would not hesitate to recommend his unit.

Early on, I established that both sensor circuits were giving different outputs (initially around 360mV and 390mV) and we thought that this differential was causing the code. Measuring over a few weeks the voltage varied slightly, but was always out by around 25mV between white and yellow circuits.

Davy was good enough to send out (to Australia!) a replacement sensor. However, when we rigged this one up it too showed a 25mV difference! As a result auto electrician decided not to fit it, but he did adjust the existing contactless TP output voltage to 400mV and 430mV so that both values were well within the range specified at idle (350mV to 600mV).

I have tried linking the two circuits at the plug (wire between white and yellow electrodes) which seemed to work initially (averaged the outputs to 370mV each) but then it threw another CEL and limp home P0221 again! That seems to indicate that the "range" referred to in the error description is the high/low voltage range rather than the difference between the circuits...or not?

Had the car home for a day and it lit up again as soon as I backed it out of the drive. Put the Unidiag on it again, cleared the codes and did another pedal recalibration. Restarted car and so far no codes, but I don't trust it to get me to the shops and back.

Have wiggled the plugs and wires at the pedal and at the Throttle body but can't recreate the error. The auto electrician recommends I take it to my maserati independent who has a factory scanner and can do live diagnostics.

Some questions I have are:

1. How much is too much for the variation between the two circuit outputs?
2. Could the ECU itself cause the circuit voltage variation of 25mV?
3. Which is the Switch B circuit referred to in the error cause description?
4. Do other users of the contactless TPS know what their voltage differentials are and can they share that information please?
5. Is 400mV too high for the voltage value at idle?
6. Could the cause be the throttle body plug and are they available separately from the TB itself?

This issue is making it hard to like the car at the moment as I think that it's going to let me down on every drive, so I'd appreciate any helpful suggestions please.

Thanks for reading! Toby

 

[jluis]

I don't know Davy implementation but a sure way to get rid of the variance on both sensors for a while is to wire one of the pedal circuits to both inputs at connector to the ecu.

The generic obd information you get from the code sometimes doesn't point in the right direction and having a main dealer connecting the sd2 to read the code and the live values measured by the ecu would help a lot

 

[Contigo]

Some questions I have are:

1. How much is too much for the variation between the two circuit outputs?
2. Could the ECU itself cause the circuit voltage variation of 25mV?
3. Which is the Switch B circuit referred to in the error cause description?
4. Do other users of the contactless TPS know what their voltage differentials are and can they share that information please?
5. Is 400mV too high for the voltage value at idle?
6. Could the cause be the throttle body plug and are they available separately from the TB itself?

This issue is making it hard to like the car at the moment as I think that it's going to let me down on every drive, so I'd appreciate any helpful suggestions please.

Thanks for reading! Toby

I know your frustration as I had issues like this until I completely rewired the Pedal Pot wiring (new connector block) and also one of Davy's pedal sensors.

1. Good question, as far as I know the circuits are there as a failsafe not as a comparison, they would only ever take an average if you did the white to yellow short trick.
2. I will measure the voltage differences of both my outputs and let you know.
3. It will relate to one of the two potentiometer circuits in the pedal sensor. Looks like output of pin 1 (2)
4. See 2.
5. No it is within the tolerance range (350 to 600mv)
6. They are wired onto the TB. I am sure you could replace them if the part is available. Try contact cleaner on it first.


DBW issues are hard to diagnose. Have you also checked the TB is ok?

Also have you checked the earths?

The white connector which connects to the pedal pot has four red wires and two grey wires. There were also two grey wires coming from the same place which are not connected to anything - they were just taped up.

pins 2 and 5 are common (5v) and pins 6 and 3 are common (0v) if you are taking any measurements. Pin 1 is the output from one of the sensors (2) and pin 4 is the other sensor output (1) all the wires should be connected though according to the wiring diagram.

Pin 2 on ECU -----> Accelerator pedal signal 2.
Pin 8 on ECU -----> Accelerator Pedal signal 1.
Pin 21 on ECU-----> TPS 5V supply.
Pin 34 on ECU ----> 5 V reference.

 

[Massa in Perth]

Thanks Phil, interested to see what values you get. On the rewire, do you know what connector block number it is, I can't find it in the manual. Where did you get a new one from and how do you do a rewire?? Sounds beyond me but not my auto electrician!

 

[Contigo]

I sourced a connector from another car which was in great condition and then wired it in usual PC block connectors. David Askew sent me the connector with wires which goes from ECU to pedal connector.

 

[Massa in Perth]

Idea. P0226 is the corresponding error code for "switch C Circuit" (appears there s no A circuit) so... if I swap the pins in the plug over (white and yellow) it will be interesting to see whether the fault code changes.

 

[Contigo]

Could do, When I disconnect the pedal sensor and fire it up without it the codes stored are P0225 (switch c).

 

[Contigo]

 

[Contigo]

One output:

Other output:

So about a 5mv difference between the two. I'd love to know what the discrepancy between the two needs to be to trigger a CEL/Limp mode. Check the voltage to both circuits , should be 5V and also grounds. I reckon this is a wiring issue.

 

[CatmanV2]

I think it must be a wiring problem. *Assuming* that the replacement sensor was tested in the same loom....

C

 

[Trev Latter]

I'd be checking the TB. When mine was failing it was throwing up pedal pot faults as well as the TB faults. In contrast, when the pedal pot was playing up, I also got TB faults showing. The issue with mine was a sticky butterfly caused by a build up of debris on the motor magnet rather than the usual tps wear issue. I would think the chances of two replacement pedal pots with similar faults are quite remote. It was about the same mileage when mine failed too. It doesn't take a lot to upset and confuse the DBW system on these cars. Downside of the early technology most likely. If yours has already been converted to a contactless tps, chances are it's ok, but I'd still check the mechanical side of things just to be sure. If the butterfly is sticking it'll be obvious when you poke it with your finger (ign off).

 

[jluis]

Sticky throttle butterfly is easy to detect.
I just tore appart a throttle body that had also had the magnet armature disintegrate and turn to debris.

Just remove the intake pipe and move the butterfly with your finger (engine off and key off)
You should feel the spring quite linearly. If it sticks or you have to push harder at some point of the travel it will be debris.

This one was also throwing pedal pot errors and at one point would not accelerate at all.

 

[Massa in Perth]

Okay thanks, very useful.

I will check the 5v feed tonight and the Throttle Body. TB is either an original or a factory replacement (not contactless). Catman, yes both pedal sensors were rigged to the same car. Phil I note your idle voltages are right up towards the max recommended limit of 600mV. Was this by design?

 

[Contigo]

Okay thanks, very useful.

I will check the 5v feed tonight and the Throttle Body. TB is either an original or a factory replacement (not contactless). Catman, yes both pedal sensors were rigged to the same car. Phil I note your idle voltages are right up towards the max recommended limit of 600mV. Was this by design?

No, that is how the sensor came from Davy, these can be adjusted but what I find is that they drop in time so I'd rather have them at the upper end of the range so they can drop back.

 

[Massa in Perth]

Okay, the feed measured 4.92V. Circuit variance is steady at 25mV (4.05V vs 4.30V). Throttle opens and closes smoothly and without hesitation. No CELs and no idea why not....

 

[davy83]

I made some measurements on this problem and I thought i would share them with you all, i have loaded one of the sensor outputs on my cars sensor (one of my own sensors) creating a difference between the two outputs and increased it until the ECU popped up an error. the sensor outputs have to be within 20mV, at 21mV i get an error, and at 15mV it works ok so the limit is around there somewhere.

 

[Contigo]

interesting so Massa had a 25mV difference between the two outputs and got a CEL but is now saying that with the variance at 25mV it does not throw an error? Davy has checked and determined that the variance is around 20mV before an error is logged.

 

[Contigo]

Davy,question that came up before about my outputs being at the high end of the idle values, do you tend to set them higher because they do drop back in time?

 

[jluis]

Be careful, 15/20 mv is a very low voltage and very likely to be falling within the error margins of cheaper multimeter's.

It's possible that massa's readings are slightly off from the real values.

Also 4.05 to 4.30V is a 250mV difference and not 25mV

 

[davy83]

Ok the other possibility here is that we are talking about two different limits here. I can test this too, i think. There will be a limit to how different the two signals can be and still be accepted by the ECU as a calibration. There will then be another possibly different limit for how far these can move from the calibrated setting before an error is given.
What i did was move one relative to the other from their calibrated state. I can try running a calibration with the two sensor outputs 20+mV apart and see if it accepts this. The tolerance to the initial setting maybe be greater than the amount it can move after calibration?
Yes I agree these voltages are really small and the measurements have to be done carefully, and indeed comparisons may be subject to the tolerance of our meters!. This is part of the reason this pedal sensor is so prone to problems, I think Maserati specified the errors based on the % of pedal travel and the effect on the engine without really thinking about what this meant in terms of the electrical output of the sensor, and created a system that is unreasonably sensitive to the sensor output changing even slightly.