2014 Transit 350 AWD terrain warning light - P2138 and U0401

[sythna]

Hi all,

I’ve recently bought a 2014 Ford Transit 350 H/R panel van, 2.2 diesel, 6-speed manual, around 64,000 miles. It appears to be the AWD / terrain mode model.

The issue is that the terrain / traction type warning light stays on.The van drives mint. No other lights (not sure if ABS light has been messed with as last MOT said it didn’t illuminate on start up).

The van drives, but I want to diagnose it properly before throwing parts at it.

A basic Launch scan is showing:

PCM fault:
P2138-00-6C
Throttle/Pedal Position Sensor/Switch D & E Voltage Correlation

ABS fault:
U0401-68-48
Invalid data received from Engine Control Module / Powertrain Control Module

The van’s MOT history previously showed an ABS-related failure for a nearside rear wheel speed sensor damaged / reluctor ring split. The previous owner says the ABS sensor has been replaced, and the van has now passed its latest MOT, so I’m not sure if the current terrain light is still ABS-related or if it is being triggered by the PCM/throttle pedal fault.

It has also apparently had a gearbox change before I bought it, so I want to rule out any AWD/transfer box issue if possible.

My questions are:

1. On these Mk8 AWD Transits, can P2138 throttle/pedal correlation cause the terrain/traction/AWD light to stay on?
2. Is the U0401 ABS code likely just a knock-on fault because the ABS module is receiving invalid data from the PCM?
3. Common causes of P2138 on these vans — accelerator pedal assembly, pedal plug/wiring, battery/earths, 5V reference, ECU wiring?
4. What live data should I check on FORScan? I’m thinking accelerator pedal sensor 1/2 voltages and all four wheel speed sensors.
5. Is there anything AWD-specific I should check after a gearbox change, or would a true AWD/transfer box fault usually show a separate AWD/4x4 module code?
6. Any known weak points on the rear ABS loom / reluctor rings / pedal wiring on these vans?

Plan so far is to clear the codes, road test, rescan, then check live pedal data and wheel speed data with FORScan.

Other MOT history that may be relevant:

The MOT history has also shown a few brake/ABS/driveline items:

* Previous MOT failure had nearside rear ABS wheel speed sensor damaged and reluctor ring split.
* Same failure also said ABS warning lamp does not illuminate.
* Previous MOTs showed rear service brakes binding and parking brake issues, including one side inoperative / cable or caliper lever stuck.
* It has had advisories for front wheel bearing excessive play on both sides at different times.
* Latest MOT pass still has minor defects for:
* Offside front outer driveshaft CV boot severely deteriorated
* Nearside front inner driveshaft CV boot severely deteriorated
* Nearside track rod end ball joint dust cover damaged/deteriorated
* There are also repeated brake pipe / brake hose corrosion advisories.
* Older MOTs showed front tyre wear/damage and lower suspension arm bush advisories.

I’m wondering if any of the ABS/reluctor/wheel bearing/brake binding history could be linked to the current terrain/traction light or the U0401 ABS code, or if the current issue is more likely just being triggered by the P2138 throttle/pedal correlation fault.

Any advice appreciated before I start replacing parts.

Thanks.

[metalworker0]

That's a lot of questions to answer.

I will just answer one for now.

Yes, faulty ABS signal will put on a traction control or terrain warning light.

Causes - Note wheel sensors take the speed of the wheel as a whole .. so tyres matter.
1.Wrong size tyres - not matched with others = less or more diameter = wrong speed reading.
2.Underinflated tyres = less diameter = wrong speed reading.
3.Reluctor ring cracked or rusted.
4.Failed wheel bearings - front wheels - i think ... wheels bearings have tone rings built in.
4.ABS sensor faulty.
5.Wiring damaged.
6.i don't know if it has a tooth counter in the diff!

Forscan will draw graphs for each wheel in "Live Data" .. using this you can compare the graphs fopr each wheel and workout what wheel is acting up .

Swapping sensors from one side to the other will tell you its a sensor, if graph line swaps to another position.

other

There are certain engine problems that will also set it off .. because the traction control will not work with engine showing

underboost or limp mode and may include throttle position faults ... but concentrate on the abs stuff forst

more other
Faulty Steering Angle Sensor
low brake fluid

all the best.mark

[sythna]

Thanks Mark, really helpful.

Quick update after doing some checks.also see attached file in pdf.

Tyres:
All 4 tyres appear to be the same size: 235/65 R16C. The rears are a different brand to the fronts, but the size numbers match. I still need to check tread depth properly and pressures on all four.

Pedal / PCM:
I cleaned the accelerator pedal connector with contact cleaner and blew it out with compressed air. That did not clear the fault.

I then fitted another accelerator pedal, but the fault is still there. It comes back within seconds of starting the engine  

Current PCM code is still:

P2138:00-AF / P2138:00-6C
Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation

The pedal live data looked smooth on the oscilloscope before changing the pedal, but the code still returns, so I’m now wondering if this is wiring, voltage, earth, 5V reference, or something between the pedal and PCM rather than the pedal itself.

ABS / traction:
ABS is still showing:

U0401:68-8B / U0401:68-48
Invalid data received from ECM/PCM

I also saw U0422:68-08 listed in ABS on one scan.

FORScan live wheel speed graphs showed all four wheel speeds rising and falling together while driving. I couldn’t see one wheel dropping to zero or spiking. In table view they also appeared to read evenly. So at the moment I can’t see an obvious bad wheel speed sensor from live data.

Other live data:
Brake fluid shows NORMAL.
ABS warning lamp shows OFF.
Traction control system status shows ON.
Steering angle was around 6.3 degrees with the wheels roughly straight, so not sure if that is acceptable or if it needs calibration. With slightly change you get to 0 and steering wheel looks straight.
AWD module shows no codes.

Mechanical issue:
I’ve also found a passenger side / nearside inner CV boot has leaked badly, with grease thrown around the area. There is also a strange grinding/binding/knocking noise on full left lock, almost like the wheel or driveline is catching or hitting something.

The latest MOT had minors for:

- Offside front outer driveshaft CV boot severely deteriorated
- Nearside front inner driveshaft CV boot severely deteriorated
- Nearside track rod end ball joint dust cover damaged/deteriorated

So I’m wondering if the full-lock noise and leaking CV boot/shaft issue could be linked to the terrain/traction light, or whether the ABS U0401 is purely being caused by the PCM P2138 fault.

I haven’t swapped ABS sensors side to side yet as I’m not fully sure how to do that on this van, or whether it’s worth doing when the wheel speed graphs look normal.

Any advice on the next best step?

Would you check:

1. Wiring from accelerator pedal to PCM?
2. Battery/earth/charging voltage?
3. Steering angle calibration?
4. Brake pedal switch?
5. ABS sensor wiring/reluctor despite live wheel speeds looking okay?
6. The leaking CV shaft/inner joint first because of the full-lock grinding?

I’ll upload screenshots of the DTCs, pedal live data, wheel speed graphs, tyre size and the nearside suspension/CV boot area.

[metalworker0]

DID i mention the throttle flaps in the manifold .

Your abs .. its passed, ignore that now

Steering angle tolerance think is the issue here

from Google AI
The acceptable steering angle tolerance for a vehicle driving straight is ideally 0°. In practice, many vehicles tolerate a sensor reading within ± 2.5° (and up to ± 5°) of center. Deviations beyond this limit can trigger traction control or ABS warnings
so i would concentrate on that for now

There is a reset procedure

But you need driveshafts etc by the looks of things .. you need to replace them, plus maybe track rod ends and anything else that is worn out , then have have the tracking done (with hunter hawkeye etc .. totem-pole looking devices).. and maybe the tracking place knows the reset procedure.. cause that will have to done afterwards

Diveshafts

Just a bit of advice .. if its done over say 100,000 miles .. i say don't replace the boots, replace the whole shaft .. if not with genuine ford, with Borg and Beck .. £70 - £100 per side. that is the price for a normal transit, not a AWD one DO NOT BUY USED

The future -- Why replace driveshafts

I hear England is to get the 20mph limits .. this will show up your drive shafts when you attempt to drive at 20mph in the usual gear you do at 30mph .. knock knock knock from the inners.
if you are doing low annual miles and ..i don't know under 2500 miles .. then repair with boots and outer cvs etc .. but if you pile on the miles .. then it's new driveshafts for you .

Note .. search term on ebay - 4x4 in the search line for driveshafts on transits, brings up more results than 4WD and AWD

all the best.mark

[sythna]

Original fault was:

PCM
P2138 — Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation

ABS
U0401 — Invalid data received from ECM/PCM

The original pedal live data before swapping looked smooth on FORScan oscilloscope, but P2138 kept returning. I cleaned the original accelerator pedal connector/plug area with contact cleaner and compressed air, but the fault did not clear.

I then got a replacement accelerator pedal with the same part number and plugged the loom into the replacement pedal while it was sitting loose on the floor. The code did not go, so I left it like that temporarily.

This morning I had to move the van. I drove it forward using the clutch only, then realised the pedal I was pressing was the original one still bolted to the van, but the plug was actually connected to the replacement pedal sitting on the floor. So there was no response from the pedal.

I then unplugged the replacement pedal and plugged the loom back into the original pedal. After that, when I started the van, it started revving by itself to around 2,000 rpm and stayed there. It turns off normally with the key, so it is not diesel runaway, but it seems to be in a failsafe/default throttle mode.

After this happened, FORScan showed a new fault:

P0653:00-A7
Sensor Reference Voltage B Circuit High

The previous P2138 is also still present/intermittent.

Live data with the original pedal plugged back in now shows roughly:

* APP_D around 34.5%
* APP_E around 16.8–17.2%
* APP1 around 1.72V
* APP2 around 0.42–0.43V
* APP2 [APP_E] showing 0.00%
* APP1 [APP_D] showing around 28.6%

These values are very similar to what I had originally at rest, but now the van is revving to about 2,000 rpm after the plug was disturbed.

One important detail: even before this got worse, if the accelerator pedal plug was left disconnected completely, the van would rev high by default. So I think revving to 2,000 rpm is its failsafe behaviour when the PCM loses or distrusts the pedal signal.

I have inspected both pedals and there are no obvious broken or bent pins on the pedal side. The replacement pedal appears to have the same part number. I now suspect the issue is on the loom connector / female terminal / wiring side, not the pedal unit itself. Possibly a loose/spread female terminal, pushed-back terminal, broken wire near the connector, 5V reference issue, ground issue, or wiring fault between pedal plug and PCM.

I do have a spare pedal connector/plug with some loom available, but I don’t want to cut/splice anything until I’m sure.

[Frag]

Who did the van belong to before you ?
Is it ex utility company,any signs of extras or modifications in the rear ?

The throttle pedal/wiring could have been intercepted for either,any onboard compressor / generator,or aftermarket speed limiter.
If it belonged to a utility company,likely with it being awd this may be your concern depending who removed any accessories

[sythna]

Belonged to groundworks and excavators company so probably didn’t have anything installed. Just used builders van. Only thing I can see if the towbar that was fitted. Not sure if I have ruined the connector as both pedal pins look okay so must have been the connector I have messed somewhere.

[metalworker0]

had to go to google ai to make any sense of acronyms:
: app_d, app, app2, app2 [app_e] , app1 [app_d]

These terms represent diagnostic parameters (PIDs) for an Accelerator Pedal Position Sensor (APPS) in a drive-by-wire vehicle, showing dual-sensor redundancy for safety. The engine computer uses these two sensors (APP1 and APP2) to cross-check pedal movement, while letters like D and E designate the specific sensor circuits.Parameter BreakdownAPP / APP_D: Refers to the primary Accelerator Pedal Position sensor (often Circuit D). It typically increases voltage as you press the pedal (e.g., 0.5V to 4.5V).APP2 / APP_E: Refers to the secondary sensor (often Circuit E). It provides redundant feedback to verify the primary signal, often running on an inverse or halved voltage scale.Bracketed terms e.g., [APP_E] / [APP_D]: Used by diagnostic software (like FORScan) to indicate the specific PID being graphed or monitored against its counterpart to check for sensor correlation.What the Computer ChecksThe Engine Control Unit (ECU) constantly compares APP1 and APP2. For illustration, if Circuit D outputs 3V, Circuit E should output a corresponding value (such as 1.5V). If the voltage signals do not match or fall out of range, the system will trigger a check engine light and enter "limp mode" for safety.For more information on diagnostic values,

Are there no throttle pids for commanded and actual in percent - that would make more sense
...... is there not something you can press on pedal; and see the numbers going up in sequence, i believe inside the pedal are segments like a digital vernier caliper. only arranged in an arc instead of a strait line.

Your results for D and E are showing what they are supposed to show according to the paragraph above .. but that's only at one throttle position

all the best.mark

[sythna]

Managed to drive van back to the house at 2000 reving RPM on a cold engine haha. Was only 6 houses down…
It seems that the engine did calm down in the middle somehow and the traction terrain error has disappeared even though it used to be back as soon as you started the van.

[sythna]

The original P2138 pedal correlation code seems to have gone for now.

The fault that will not clear now is:

P0653:00-A7
Sensor Reference Voltage B Circuit High

This stays even with the accelerator pedal disconnected.

With the pedal connected, the pedal live data seems stable and pressing the pedal shows smooth movement. Wiggling the pedal connector/wires does not change the live data.

At rest, plugged in, I’m seeing roughly:

* APP_D around 34%
* APP_E around 16.86%
* APP1 around 1.71–1.72V
* APP2 around 0.42V
* APP1 [APP_D] around 28%
* APP2 [APP_E] 0.00%

Those are basically the same values I had before touching/swapping the pedal.

With the pedal unplugged, some of the FORScan APP readings change quite a lot, for example APP_D and APP1 voltage go high, while APP2 drops very low. I assume these are invalid/open-circuit or PCM fallback values rather than real pedal position. The van also appears to rev high when it does not have a valid pedal signal, but I’m not 100% sure if that is normal failsafe behaviour on these vans or another symptom of the current 5V reference fault.

I tested the accelerator pedal loom plug with ignition on, engine off, pedal unplugged. Readings were:

* Blue/grey: 5.02V
* Blue/white: 0.03V
* Yellow/green: 0.02V
* Green/purple: 0.02V
* Orange/unknown stripe: 3.23V
* Last wire: 5.02V

So I seem to have two clean 5V feeds, grounds/low wires close to 0V, and no obvious 12V at the pedal plug. This makes me wonder if the P0653 is not actually the pedal connector now, but another sensor on the same 5V reference circuit.

I also checked the pedal connector/female plug visually. No obvious broken pins on either pedal, and the replacement pedal number matched. I do have a spare pedal plug/pigtail if needed, but I have not cut or spliced anything yet.

Mark asked about throttle PIDs. I have not found the exact commanded/actual throttle percentage PIDs yet, but I will look again in FORScan. The PIDs I have been watching so far are mainly APP_D, APP_E, APP1 voltage, APP2 voltage, BAP voltage, boost pressure %, RPM/DRPMIS, and wheel speed sensors.

Wheel speed graphs still look even on all four wheels. I could not see one wheel dropping out or spiking.

Does P0653 staying with the pedal unplugged suggest I should stop focusing on the pedal and start unplugging other 5V sensors one at a time, such as MAP/boost sensor, fuel rail pressure sensor, DPF pressure sensor, EGR/throttle body, A/C pressure sensor, etc., to see which one allows P0653 to clear?

Any idea which sensors share “Sensor Reference Voltage B” on a 2014 Mk8 2.2 Transit 350?

[metalworker0]

I know one thing .. i cant focus on the shear number of problems and codes per question .

so, i say focus on one problem at a time, you've gone from steering angle sensor .. you've left that behind, that was the one problem i was focusing on .. then you're back onto the pedal ..
if you just want to do just the pedal for now that's fine with me. you see you are asking all this , then someone else comes along with a different problem in the forum for another van and it turns into a head scramble when i get your multiple problems. i would imagine that anyone else reading would have similar information overload.

all the best.mark

[sythna]

Fair point Mark, apologies — I’ve made the thread too confusing by jumping between ABS, steering angle, pedal, AWD and mechanical issues.

Let’s ignore the steering angle, ABS, AWD, wheel speeds and CV boot issue for now. The steering straight does read 0 degrees now. I think I just had it a bit tilted with just a minor touch it went to 0 and stays there with no drops or spikes in degrees btw.

The single issue I want to focus on is now:

P0653:00-A7 — Sensor Reference Voltage B Circuit High

Current facts:

- Original P2138 pedal correlation code has now gone due to the new code.
- P0653 is the only main PCM fault that will not clear after I messed with swapping pedals and forgot to plug it in.  
- P0653 stays even with the accelerator pedal unplugged.
- Putting original or Replacement accelerator pedal with matching part number did not fix it.
- Pedal live data moves smoothly and returns to the same resting values.
- Wiggling the pedal plug/wiring does not change live data.
- Pedal plug voltage test with ignition on, engine off, pedal unplugged showed two 5V feeds and no obvious 12V at the pedal plug.

So I think the accelerator pedal itself is probably not the fault now. Does the van need to relearn anything here?

My question is just this:

On a 2014 Mk8 2.2 Transit, what sensors/components share “Sensor Reference Voltage B” for P0653?

Should I now unplug other 5V sensors one at a time, for example MAP/boost sensor, EGR/throttle flap, DPF pressure sensor, fuel rail pressure sensor, A/C pressure sensor, etc., to see which one allows P0653 to clear?

I’m trying to find the correct next step without guessing or cutting the pedal loom unnecessarily.

Thanks again, and sorry for the information overload.

[metalworker0]

Yes start unplugging sensors, sounds like an idea, ive seen Diagnose Dan (youtuber) doing that and he found the 5 volt on one other sensor causing faults with another.

Then was able to narrow it down to the wiring for that other sensor, but then again .. his 5 volt in the a whole part of the can bus system was down on voltage.

These techs now have a app installed on their computers that they pay monthly for .. its called "Alldata"

it has the diagnostic trees on it, visual flowcharts that map out a sequence of logical, yes/no questions to reach a specific conclusion or solve a problem, also the circuit diagrams that they can highlight specific circuits in a different colour.. elimination processes .. that thousands of garages have contributed to, makes life easy for them, but not for us .

they have that , we don't, all we have is google AI, which with complex problems you have may be the only help you get .

all the best.mark

[sythna]

Quick update.

Had a mobile diagnostic guy come out today. He thinks the fault may be ECU/PCM related.

He said it looks like someone has been around the ECU before. There was an extra ground wire added, even though he said the original ground tested fine. Some clips around the ECU area were also broken, so it looks like it has been disturbed previously.

Current fault is still:

P0653:00-A7 — Sensor Reference Voltage B Circuit High

The original P2138 pedal correlation code has not returned. Pedal readings still look smooth and return to rest, and changing the pedal did not fix it.

I now need to decide where to take it next.

Option 1: take it to an ECU specialist who does ECU testing, repair, cloning and mapping.

Option 2: take it to an independent Ford specialist. I spoke to one and they said they would usually prefer fitting/replacing the ECU rather than repairing it, as repaired ECUs can potentially fail again.

What would people recommend on these Transits?

Is this the sort of fault better handled by an ECU specialist first, or would a proper Ford specialist be the better route because they can check the van-side wiring/loom as well?

I’m trying to avoid paying for an ECU repair/replacement if the issue is actually in the loom or a sensor circuit.

[metalworker0]

Ecu's Pcm's are the last things you should be looking at .. because they mean spending big money.

P0653:00-A7 - your can bus system is over voltage on the 5 volt

Well, what happened about (YOUR IDEA) of pulling random sensors and seeing if that goes away?

This is what google AI says

And you were more or less acting in the right way

Check for Sub-Codes: Use an OBD-II scanner to read any accompanying codes (like P2138 or P0122) . These often point to the exact failed sensor.Unplug & Isolate: Disconnect engine sensors sharing the 'B' circuit one by one . Measure the reference voltage with a multimeter; if the voltage drops back to 5V when a specific sensor is unplugged, that sensor is faulty.Inspect Wiring: Visually trace the wire harnesses from the sensors to the ECU for signs of chafing or corrosion .

You know, some people have followed the garage advice .. or the diagnostic guys advice .. and gone on to spend a lot of money before the fault was found,.. it's easy to fire the parts cannon, when its not your money!

all the best.mark