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Discussion Starter · #1 ·
Hey guys, first time posting and i need some help, Im working on troubleshooting a buddies 2016 ST and its throwing P08AA and sometimes some other low voltage codes as well. He already replaced all three clutch sensors, slave cylinder and I bled the system. I've checked grounds, traced all the wiring to the sensor, which is the one behind the battery box and all three wires wind up at the PCM. I checked continuity through all three and they all show 0.0 ohms and I have 0.1 v of voltage drop. As soon as i plug the PCM in and follow the pinpoint test i have voltage on the CPP wire when it says I'm supposed to have none, and i have nowhere near the specified resistance on all three wires. (2600 ohms) workshop said it should be 10k or more for this test. When i checked reference voltage it asked for 4.5 to 5.5 volts and I got exactly 5.
As far as PCM condition goes from a visual side, its corroded, the CPP wire enters at the spot with a ton of corrosion, the box its stored in is not sealed anymore and the fender liner is missing. I'm pretty certain that that is my problem but i wanted to ask for more opinions as all my tech friends wont even touch the thing or offer any advice and i need to come up with a solution soon.
this car has also had some other work done to it, and it just had a stock motor put back in after being big turbo tuned and built, and its having some other quirks here and there that also lead me to think that maybe the tune was never completely erased.
Questions, Comments, I'll be waiting for them!
 

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2017 Kona Blue ST1
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So you heading in the right path.
So the CMCPDPS (good lord btw) - or (clutch master cylinder push rod position sensor) is a simple 3 wire hall effect sensor.

C1690 Pin 3 is the 5 VDC VREF from PCM connector C1381B Pin 11 at the S157 splice point. It shares this reference voltage with the A/C Pressure Transducer, Turbocharger Boost Pressure, & Crankcase Ventilation Monitor. It should not read lower than 4.8 and no higher than 5.5 VDC.

C1690 Pin 1 is the CPP SIGRTN (PCM Ground) to PCM C1381B Pin 17.


C1690 Pin 2 is the actual sensor output back to PCM C1381B Pin 76 CPP.

Usually when dealing with corrosion on copper it will provide a voltage drop because of the extra resistance, however you have checked both continuity and resistance.

PCM plugged in and C1690 CPP sensor unplug the should read between the suggested VREF voltages Pin 1&3.
C1690 plugged back in with Pin 2 de-pinned test the sensor output for normal function Pin 1&2. If sensor output is normal and voltage is being detected on Pin 2 wire from PCM then you most likely have a damaged PCM module.
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J
 

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I have the same exact issue, I changed the CPP sensors but there are 2 and one other member had the same issue and ended up changing it for the third time to get a good working sensor.
I haven't changed the the upper side sensor yet, its pain in the ass but I did change the master cylinder pedal assembly when I put in a new clutch.
You can test it by reading the CPP switch readings should should 50-100 and 0-50 something like that mine is either 66.7 or 100%.
I am guessing your cruise control wont turn on too as safety measure?
 
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Discussion Starter · #4 ·
I have the same exact issue, I changed the CPP sensors but there are 2 and one other member had the same issue and ended up changing it for the third time to get a good working sensor.
I haven't changed the the upper side sensor yet, its pain in the ass but I did change the master cylinder pedal assembly when I put in a new clutch.
You can test it by reading the CPP switch readings should should 50-100 and 0-50 something like that mine is either 66.7 or 100%.
I am guessing your cruise control wont turn on too as safety measure?
I have the same exact issue, I changed the CPP sensors but there are 2 and one other member had the same issue and ended up changing it for the third time to get a good working sensor.
I haven't changed the the upper side sensor yet, its pain in the ass but I did change the master cylinder pedal assembly when I put in a new clutch.
You can test it by reading the CPP switch readings should should 50-100 and 0-50 something like that mine is either 66.7 or 100%.
I am guessing your cruise control wont turn on too as safety measure?
Exactly the same,66 percent at top, and 97 percent at bottom, and cruise doesn't work.
 

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Discussion Starter · #5 ·
So you heading in the right path.
So the CMCPDPS (good lord btw) - or (clutch master cylinder push rod position sensor) is a simple 3 wire hall effect sensor.

C1690 Pin 3 is the 5 VDC VREF from PCM connector C1381B Pin 11 at the S157 splice point. It shares this reference voltage with the A/C Pressure Transducer, Turbocharger Boost Pressure, & Crankcase Ventilation Monitor. It should not read lower than 4.8 and no higher than 5.5 VDC.

C1690 Pin 1 is the CPP SIGRTN (PCM Ground) to PCM C1381B Pin 17.


C1690 Pin 2 is the actual sensor output back to PCM C1381B Pin 76 CPP.

Usually when dealing with corrosion on copper it will provide a voltage drop because of the extra resistance, however you have checked both continuity and resistance.

PCM plugged in and C1690 CPP sensor unplug the should read between the suggested VREF voltages Pin 1&3.
C1690 plugged back in with Pin 2 de-pinned test the sensor output for normal function Pin 1&2. If sensor output is normal and voltage is being detected on Pin 2 wire from PCM then you most likely have a damaged PCM module.
View attachment 384743 View attachment 384744 View attachment 384745 View attachment 384746

J
Yes I had 5 volts on 1 and 3, pin two has like .07 volts to it, which according to the manual indicates a short circuit, another reason I'm narrowing it down to pcm, is I actually did an overlay of pin 2 to the pcm, and I changed absolutely nothing, normally if there's a short in a system like that and overlay at least starts to clean things up. It's interesting that pin three shares a splice with the turbo output as he also claimed his boost gauge was all over the place, didn't see anything off but it could be sporadic
 

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2013 Ford Focus ST1
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I have the same exact issue, I changed the CPP sensors but there are 2 and one other member had the same issue and ended up changing it for the third time to get a good working sensor.
I haven't changed the the upper side sensor yet, its pain in the ass but I did change the master cylinder pedal assembly when I put in a new clutch.
You can test it by reading the CPP switch readings should should 50-100 and 0-50 something like that mine is either 66.7 or 100%.
I am guessing your cruise control wont turn on too as safety measure?
It sure is a pain in the ass to get to the upper clutch pedal sensor without taking the pedal assembly out of the car. I had a clutch replacement done about a year ago (including all hydraulics) and my shop didn't attach the upper sensor to the pedal (although it is still connected and no defective). As a result I now have to press both clutch and brake pedals to start the car and also now have to hold the start button until the engine fires. Cruise control still works normally though thankfully, because I simply can't reach the upper sensor. :cautious:
 

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Yes same it turned the car into a old school jaguar, Hold the brake in and clutch and hold the start button until it starts lol
I dont mind it but the thing is it says press clutch and brake but I dont have to press the clutch it thinks its pressed or something.

Anyway I will take buy new sets of sensors and try again. If not I am guessing its a PCM issue.
How much does a PCM programming and a used PCM go cost? any idea?
 

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Discussion Starter · #8 ·
Yes same it turned the car into a old school jaguar, Hold the brake in and clutch and hold the start button until it starts lol
I dont mind it but the thing is it says press clutch and brake but I dont have to press the clutch it thinks its pressed or something.

Anyway I will take buy new sets of sensors and try again. If not I am guessing its a PCM issue.
How much does a PCM programming and a used PCM go cost? any idea?
I'm gonna make a guess of around 500 or more for a pcm, not sure on programming
 

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Just to be clear do we need to marry the AP before any kind of PCM swap?
 

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Yes you will need to unmarry the AP and update its firmware before installing onto the new PCM. You will likely need to inform your tuner as well.

J
 
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yes, both are new and in place but didn’t solve my issue sadly
I'm afraid it has to do with wiring at this point. haven't gotten a chance yet to look at mine.
 

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I haven’t had the time either but maybe mine is a wiring issue and i probably accidentally cut wires with the grinder when i was grinding this part off to fit the assembly along with the sensor already in place, i’m hoping that’s the case 🤞🏽
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