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KW Diagnostics, Winsford (2026)

15/04/2026

Here I had a car in for an intermittent EML and limp mode, apologies I can't remember what the DTC was but it was a Throttle Pedal position sensor 2 plausability fault.

Initially I couldn't get the car to fault. And initial testing via live data of both position sensors for the Throttle Pedal looked to be perfect.

When I went and test drove the vehicle, the fault code or EML didn't appear but there were a few minor deviations in the datalogging graphs. When I returned to the workshop, I again tried to get these deviations to appear.
I stopped, operated the Throttle Pedal many of times and it was perfect again. Initially I thought it was due to vibrations or going over bumps etc but this wasn't the case.
As I went to back out of the workshop I noticed the graphs deviate again. I noticed it occured when I was actually braking.

So I switched the engine off and had the ignition on, operated the brakes and finally found when the fault was occurring, during braking only.

So what was causing this, what appeared to be, signal interference?
My first thought was to disconnect all sensors connected to the brake pedal operation, (Brake pedal switches, brake pressure sensor, brake vacuum sensor) but this made no difference.

I had a look at the wiring diagram to find a connection between the brakes and the Throttle Pedal but there wasn't any. I noticed however there was another plug for the Throttle Pedal between the Pedal and the ECU, I thought I should pay it a visit, and this is where I found my fault.

Someone has worked on the car in the past, had somehow got this plug connector jammed solid between the HVAC housing and the bar that runs across the bulkhead for the brakes. What was happening was everytime the brakes were operated, the bar would turn and cause the plug to flex, meaning that the connections would spread slightly, raising the signal voltages higher than they should be.

Moving the plug to the correct location fixed the fault.

Some of the most challenging faults are man made faults in my experience and this demonstrates the importance of fitting wiring and plugs back to where they belong.

10/11/2025

Here we had a car in for a complaint regarding stop-start interrupting the radio when the engine restarts. During cranking the radio would briefly go off for a split second causing an irritation for the customer.

Initial global scan reveals no fault codes in any control module on the car. Testing the supply inputs to the radio to see what was going on, I found that the ACC On input for the radio was dropping out during engine cranking. This switch supply is fed from the DC-DC converter and has two modes of operation, during IGN on or engine running, the feed is passed directly from the ACC relay output via the DC-DC converter, however during engine cranking, the ACC relay opens disrupting the 12v supply to various components, the DC-DC converter is supposed to take over by supplying the voltage momentarily to the radio.

The DC-DC converter is located behind the top of the dash so doing testing there would be very difficult.
Looking at the wiring diagram we can see that the DC-DC converter gets a switched input from the starter motor relay to know when the engine is cranking.
Connector MC11 in the wiring diagram looks to be the best and closest place to test. I found that with IGN on it had around 4.5V and the ground control of the starter relay had 3.5V so I knew there was a problem.
Monitoring the voltage during cranking showed that the circuit was never grounded so the Voltage stayed the same, meaning that the DC-DC converter wasn't getting its ISG Start signal, hence why it never took over providing a supply to the radio.

Temporarily I jumped a wire from the relay to the pin for the ISG Start input to prove the system works and it did, no more radio going off during cranking.
The wiring runs through the bulkhead from the engine bay so I decided to take the PCB block out of the fuse box first to check if the wire was connected to the relay connector.
This is where the fault is found, a broken wire in the fuse box, after repairing it everything works as expected.

It took me two attempts to diagnose this, as I was looking at a wrong wiring diagram initially and something wasn't adding up 😅 it wasn't until I went directly on the manufacturers portal that I realised that I had been working with the wrong info.

26/08/2025

We had a car in with intermittent long crank and intermittent running issues.

Fault codes P0344 Camshaft sensor circuit erratic and P0340 Intake camshaft sensor circuit - No signal

Upon visual inspection I saw two brand new aftermarket Cam sensors fitted, which I thought was going to be the problem.

Upon scoping the sensor I found I had a perfect signal. Stress testing the loom and plug connector to the ECU I could replicate the running problem and also see that the Cam signal was indeed becoming erratic.
I scope the sensor ground and 5v reference as well, the 5V reference was perfectly fine but the ground was going open circuit as well.

The fault would occur when wiggling the ECU plug connector. Upon removing the plug from the ECU I found the pin grip didn't exist for niether thr signal wire or the ground wire. A fine adjustment to both pins fixed the faults and now no matter how much the connector is wiggled the waveforms stayed perfect.

Also had a BMW for intermittent drivetrain fault. 200D0B Transmission status signal implausible, D3557A signal invalid were the only codes.
Initially I didn't understand the fault code so use ISTA to find out what the codes were referring to. The car wasn't happy with the clutch position sensor.

With this information, I looked at the live data and took it for a roadtest, and found that the car kept seeing the clutch being operated when it wasn't.
There's two sensors built into the clutch position sensor, one feeds a signal to the FRM and the other to the ECM. I decided to scope both signals and monitoring when fault occurs via live data on the scan tool, to my surprise there was absolutely nothing wrong with the signals outputted to either control units?
I was expecting some sort of signal interference to which there wasn't any. Deciding next to test powers and grounds to both modules I used live data to find the ECM and FRM was dropping below 12V when fault was occurring.

So I checked the 12V battery and found 14V so I know the car is losing 2V somewhere. Voltage drop testing showed the fault was in the ground Circuit, further testing led me to the ground cable from chassis to the gearbox.
Upon repairing the bad ground the fault was fixed.
Funny thing about this was the scan tool shows the voltage in top right corner and I failed to even notice it, lesson learned. Just it didn't occur to me at the time due to a very isolated fault with no other issues.

19/01/2025

Sorry I've not posted in months, I've been mental busy, had some really good jobs but never got the time to document them to share.

Anyway I've been busy working on a project in my spare time and trying to learn something new.

Speaking of something new, this week was the first time of using Tesla software after a SCCM was replaced. It's radically different to any other software I've used in the automotive industry. Thankfully Tesla provide excellent, clear and precise technical information, and it was very easy to set up.

Also had a customer in to have a new key coded on their new car, they had a missing key blade, but whilst here I was asked to look at an intermittent issue for the radio going off.
Fault was traced to a key blade shorting out in the head unit 🤣 was quite amused that we solved the mystery of the missing keyblade and fixed the radio at the same time.
Also worked on my first Bentley and Ferrari last weekend, the Bentley had a no comms issues to the air suspension module, fault was traced to a bad CAN L signal from a CAN block. And Ferrari had no wheel speed signal from a rear wheel, nothing exciting but was different
Anyway, hope to start posting more in a few weeks

17/10/2024

Here we had a car presented for a heater blower motor being inoperative, is it not working because it's a failed blower motor? Or do we have something entirely different wrong with the vehicle?

A global fault code read revealed a fault in the AC control module. U107600 Local data bus, electrical error.
So first of all a check of a wiring diagram was required to make a plan for testing, the fault code implies there's physically a fault with part of the communication network connected to the AC panel.

Looking at the wiring diagram, specifically the blower motor as that is the fault it's here for and the component we know isn't working, the blower motor is connected to the LIN network which is shared with 2 other components as well as the blower motor control unit, the Air Quality Sensor and the AC Pressure sensor.

So this leads to multiple possibilities as to why the blower motor isn't working, the AC panel being faulty, any of the 3 components listed above or a wiring fault.
A quick look at live data for the 3 components shows none of these components are broadcasting any data.

With this information we can carry out a test on the LIN network for these components, the AC pressure sensor was perfect testing place for this as it was the easiest to access.
After scoping the waveform, it was clear we do have a physical LIN network fault, in this case it made perfect sense to unplugged the AC Pressure switch as we are testing here already. As luck would have it, the LIN network returned to normal function and the blower motor is working again whilst the switch is unplugged.

So the blower motor inoperative inside the car actually needs a AC pressure switch behind the front bumper

05/10/2024

300 mile round trip to look at an intermittent High Speed CAN Bus fault for a friend in the trade.
It was originally a full no comms situation when I was asked about it, the car didnt run and no module on the powertrain responded to the scan tool, but a few days before the car came back alive and ended up being intermittent under hard acceleration, the car would lose drive and lots of warning lamps on the dash would illuminate.

Sometimes the fault wouldn't appear but using my Pico we were able to spot that there was a very brief short to ground on the CAN H of the powertrain network even though this didn't cause any issues, it had to be shorted for longer to bring the warning lamps on and cause the car to stop driving.

This was a tough one to track down, as originally I was fixated on the wiring contact points and modules under the bonnet due the tech saying the car came back alive when they were under the bonnet, so theory was that something was disturbed.

I could never get the car to fault in the workshop, so i had to resort to looking for contact points of the wiring loom around the vehicle that housed the Power train network wires.
After ruling out the bonnet area and 4WD module, I proceeded to check behind the dash for more contact points and found my fault, the CAN H was very slightly rubbing through on the bracket causing our intermittent short to ground.

As you can see in the photo, the area that had rubbed through is barely noticeable, I cut some tape back to be able to show more clearly the insulation has slightly rubbed through

27/06/2024

This Volvo was setting an intermittent P0137 O2 sensor 2 signal circuit low.

Using the picoscope utilising Masks made absolutely 'short' work out of this job!

Using the scope and some logical manipulation of the wiring meant finding the source of this fault easy enough, the signal wire was shorting against the EGR pipe. A repair of the wiring and a modification done to the loom and this one is fixed for good.

14/06/2024

Happy Friday! Been a great Friday for me thanks to the first and the last job of the day.
A 70 plate Leon none runner, told poss transmission module faulty.
After a code scan, several fault codes for no Comms with the Transmission control module and it didn't respond to the scan tool.
This was traced to a corroded power supply, wiring repaired and all fixed.

Last job of the day got me a fix on a very troublesome intermittent none start.
I couldn't get it to fault on me initially but this afternoon it finally faulted, after pushing the car into the workshop and setting my scope up, it started and ran again 🤣

The fault was open circuit DTC of the fuel pump control module from the ECM. I had access to the fuel pump module but as stated fault disappeared, I tried wiggle test at the fuel pump side with no joy.
Also tried at the ECU with no joy. Initially I started to remove the security bolts to get access to the ECU so I can inspect the plug connectors.
Luckily I realised I hadn't studied the wiring diagram properly to check for any additional connectors and due to feeling frustrated that the fault was no longer present I was skipping an important step.

Anyway, after I saw there's another connector between the fuel pump module and the ECU I decided to check that connector to see if I can replicate the complaint from there.
Sure enough, as you can see from my oscilloscope trace, the circuit was intermittently going open circuit at the fuel pump module as I gently wiggled the wire at the plug.

I expected a lose pin fitment as I've been having a lot of these the past year. But it was infact what looks to be a fault from factory. The male pin wasn't all the way in the plug when the lock on the plug was closed in, this was causing the two terminals to just about to be making contact. There's absolutely no signs at all anyone has ever been here so I'm convinced this is probably a long term problem

26/04/2024

It's been some months since I've last posted, going to try and make a bit more effort going forward. Not really got any exciting case studies to post but couple of jobs I've had in this week.

First was an Audi with a rear AC panel inoperative. A scan revealed there was missing communication with this panel.
Looking at a wiring diagram, it just has a power, ground and LIN signal. Having checked these all voltages were present, however disconnecting the plug the LIN circuit went to zero volts, meaning that there is an open circuit on the communication wire.

The wiring diagram showed two other LIN components, these were working so I only had to check the wiring between the splice and the panel. Luckily when I removed the trim panel I spotted that someone got a bit heavy handed cutting the tape around the loom cutting through the LIN wire.

Also was asked about a Transporter that was intermittently logging. P007C00 charge air cooler circuit low. I said it is most likely going to be a wiring fault.
Visually checking the wiring from the sensor revealed the wiring to be fowling the wiring for the fuel temperature sensor.
The charge temp sensor signal wire has been rubbing with the ground wire for the fuel temp sensor causing the intermittent short to ground.

Also got round to fixing a few PS5 controllers that were suffering from stick drift, some new potentiometers soldered in saving some money 😂

06/01/2024

I was asked to do a 6hr round trip to look car that's been a none runner for 3 months, with what was suspected to be a Powertrain CAN Network fault, in that all modules are offline on the powertrain network.
This one turned out to be a good case study on why sometimes piercing probes are my preferred method and in this case saved me a lot of time.

Initially I checked powers and grounds to the ECU as it was already accessible, they were perfectly fine. This vehicle has a Gateway module so the Powertrain network was tested at the ECU, the signal looked good but the BUS was full.

I tested the CAN BUS signals at the gateway and checked the messages were in sync at both ends, this proved to be the case and ruled out an open circuit at least on the wiring side. One thing I did notice here though when I disturbed the Gateway the voltage level fluctuated and I found a loose PIN fitment, after rectifying this, the issue wasn't resolved.

After doing a few more tests I made the call to break the CAN wires to the ECU and join it directly to the Gateway so I could isolate the rest of the network with hope to restore comms to the ECU.
However when I broke the connection to the rest of the network at the ECU I then found that the ECU CAN L was flat lined at 0V but CAN H was functioning correctly. I then used a back probe to make a connection to the ECUs PIN and re-join it into the network this way. The car then started and ran, full communication was restored with all control units.

The fault then being a poor pin fitment to the ECU on the CAN L wire, the full BUS was due to no response from the ECU. After replacing both CAN wires and PINs the car is now fixed.

The thing with this, is if I used a back probe pin at the ECU I would have temporarily fixed the network and found a perfect CAN signal and no full BUS, which then would have then possibly lead me to spending many hours of frustration in a different direction. So the piercing probe was a huge help in this case.

11/11/2023

I was asked to look at a Range Rover Sport that had broken down. The Instrument cluster was dead and pretty much everything else in the car was.

The first thing I did was plug in my OBD breakout box to establish if there's any power and to see if there's any CAN activity.

Upon noticing Pin 6 + 14 of the DLC appeared to have no activity, I double checked by pressing the ignition switch which should at least wake the modules up, but still there was nothing.
So I checked the voltages of the CAN H and CAN L for the Power train network. Both pins were showing 1.96Volts. So I disconnected the battery then did a resistance measurement of the two lines, I found I had around 3ohms.

Knowing there is no gateway between the DLC and the vehicles powertrain network I was happy I have great direction with the vehicles problem, we have a CAN H+L shorted together fault, causing all the powertrain modules to be offline, unable to communicate with each other.

As you may well know, this fault could be anywhere, anywhere within the CAN wiring, or any one of the 18 control modules.

I was told by a tech the Transfer box was just very recently replaced, and this module is on this CAN network. So this was quickly disconnected to rule it out first, this wasn't causing our problem.

So it's time to make a plan to dramatically reduce the amount of work and and amount of time involved in finding this short circuit.
With a wiring diagram at my disposal, my first part of my diagnosis was to reduce the number of modules and wiring I would have to go looking at.

Luckly we have a quick and easy connector to disconnect labeld C12. Disconnecting this got rid of my short circuit at the DLC breakout box.
This meant we can take 14 of the control modules out of the equation and a huge amount of wiring.
This leaves us with 4 control modules and the wiring at the back of the dash and under the bonnet.

Not being able to use the DLC as a location for testing, I moved my multimeter to the plug connector that I have just disconnected on the side that still has our fault.

The quickest and easiest modules were disconnected, PCM and ABS, this made no difference. I was now down to the 2 remainer modules in this network, either the headlamp leveling module or the ACC control module and still the whole loom under the bonnet.
Once the grill was removed to access the ACC module I have found my fault.
The wiring was fowling the fan exposing the copper wiring of 3 wires, with the CAN H making contact with the CAN L wire resulting in the short circuit and a dead car.

Car is now back up and running with no parts replaced.

Sorry about the lack of photos in this one.

25/10/2023

I was asked to give a second opinion on this vehicle as they were quoted £1,600 to replace the ECU to fix an intermittent issue where it would have various warning lamps illuminated, loss of power and unable to drive above 10mph. This typically happens within an hour of driving.
Unfortunately there were no codes in the ECU when I got hold of the car, and no reports of previous DTCs which meant I had to drive it for 40 mins until it faulted.
When it faulted the car lost all power, RPM restricted to 1,200 and I couldn't get over 14mph.

After getting it back to the workshop, I scanned the fault codes, I had 3, P0222 Throttle postion sensor 2 signal too low, P0122 Throttle-Valve position sensor signal too low and P0651 Sensor reference Voltage B open circuit, this gave me a great direction to go in to diagnose the fault. After looking at the live data when the fault was occuring, the throttle valve signal would drop to 0, I was confident this would be a wiring fault.

I had some trouble getting the car to fault in my workshop, I decided to hook the scope up to the 5v reference circuit for the throttle body to easier see when the fault was occuring. I was able to see the 5V reference being pulled down to ground very regulary although very briefly when pulling away, but codes would only trigger when the circuit was shorted for a longer period of time, the very short bursts of shorts wasn't enough to trigger fault codes or notice any running issues.

With the understanding of the fault, it was a case of looking for contact points in the loom for where it may be shorting out.
I found that the 5V ref was shorting on the top of the gearbox cover. Wiring repaired and modification made to ensure it doesn't happen again.

Thankfully the £1,600 ECU wasn't fitted before I was asked to look at it.

KW Diagnostics

15/04/2026

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17/10/2024

05/10/2024

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