Ford Focus MK2 - P2121 Fault Code - Pinouts required

[ecooney]

Hi all, 

 

I have a 2005 Ford Focus 1.6 petrol automatic. 

I have an engine light on and have read the codes and it's throwing a P2121 fault (Throttle/Pedal Position Sensor/Switch D - Circuit Range/Performance)

I wanted to test the TPS and APP sensors and see they have 6 cables each. 

Would anyone have a test procedure for these? 

It seems there are 2 earths, 2 constant 12v (not tested with pedal connected yet), a 5v reference and a 0.5v at rest on the APP sensor. The 0.5v signal moves in a consistent curve to around 3.2v with the pedal fully pressed and back to 0.5v resting. 

Also, someone has already been working on this sensor by the looks of it which makes me suspicious. The centre "security pin" on the torx screws has been removed to allow it to be opened and a couple of plastic tabs are broken. 

 

If someone could point me in the right direction on how to best test this circuit and connectors I'd be most grateful. 

 

Also, excuse my lack of knowledge, what is the Switch D? Something to do with the PCM or am I missing something? 

[ecooney]

I've just tested the APP sensor when its connected and see the following. 

 

Green/Yellow Cable - 12v

Grey Cable - 12v

Black/Yellow Cable - Ground

Brown Cable - Ground

White Cable - 0.5v 

Yellow Cable - 5v

 

It seems incorrect for this sensor to have 12v on 2 of the pins????

 

[Hobgoblinpie]

I had this exact same fault on my car. It turned out to be that the ground that was connected to the post on the car had been fiddled with and was 'contaminated' (it had been taken from its usual post, and the bare wires had been wrapped around onto another ground post). The mechanic fixed it by attaching the wires to a proper connector, and reattaching it to the proper post. 

I can't help with locating it, but this is how the mechanic explained the solution to me. When I bought the car it had had the AC completely redone a couple of months prior, so I assume they bodged it and screwed up the APP sensor ground at the same time.

[Tdci-Peter]

12 hours ago, ecooney said:

Grey Cable - 12v

Black/Yellow Cable - Ground

Brown Cable - Ground

White Cable - 0.5v 

Yellow Cable - 5v

 

It seems incorrect for this sensor to have 12v on 2 of the pins????

The grey cable is the output to the PCM (ECU). The drawing says "PWM", so it is likely to be a square wave switching, but the average voltage as read with a meter should follow the pedal position.

The white cable is the output to the IC (Instrument Cluster). This one is a 0-5v signal.

If when moving the pedal, the voltage on the White wire follows the movement is a reasonable way, but the Grey one stays constant, then that suggests a fault in the APP.

Diagnostic systems like Forscan can usually monitor the two APP readings. There are two for safety reasons.

Part of wiring diagram below. C118 (at the bottom) is to the IC. The box on the left with the fuses is part of the PJB (passenger fuse box). The full schematic (132 pages!) is here:

https://www.fordownersclub.com/applications/core/interface/file/attachment.php?id=42087

This APP can be found on pages 49 (non-vvt) or 51 (ti-vct)

[JW1982]

On the Focus MK2/MK2.5 the electronic throttle pedal is not connected to the PCM. It is connected to the instrument cluster. The instrument cluster converts the PWM signal of the electronic throttle pedal to a CANbus signal and transmits this signal to the PCM. The instrument cluster is also responsible for the throttle response (which can be improved by configuring the car as an automatic and selecting "Sport").

Throttle pedal related DTC codes are often caused by the classic instrument cluster problem that is caused by cracked soldering connections. I have seen this many times before.