Latest News:

autotechnician - serving the independent workshop - logo

Case study: Faulty Ford Focus

Case study by Des Davies AAE MIMI, Top Gear Motor Services Ford Focus MK2 1.6 16V, Engine code SHDA
Intermittent non start, no crank
Fault codes in PCM P1260-21, U0001-E1, U0140-61, U0121-A1

A customer complained of an intermittent no crank, with key in cranking position, from initial start in the morning, with no other symptoms given. Also, the traction control light would sometimes, but not always, be displayed on the dashboard. The RAC checked the vehicle and reported a no communication fault on their scanner.

Why do I always get these intermittent faults other garages are scared of? Yes, they are time-consuming and very challenging, but they can also give you a great deal of satisfaction as well.

There was no check engine light or any other warning lights on dashboard. I connected my scanner to the OBD port to check for fault codes and I had many communication codes, from the PCM, ABS and instrument cluster modules.

This vehicle would run for a week or more again before it became a no crank/start problem. Every time it came into my workshop the vehicle was running, not a good time to test! I needed this vehicle to be left at my disposal to try to get the vehicle not to start so that I could run tests to verify the fault and hopefully fix the underlying fault/s.

Figure 1

Codes retrieved from vehicle

P1260 – Theft Detected Vehicle Immobilized (Ford) U0001 FORD code, possible causes:

Faulty Power Steering Control Module (PSCM)
Power Steering Control Module (PSCM) harness is open or shorted
Power Steering Control Module (PSCM) circuit poor electrical connection

Symptoms of fault code U0001: Check Engine light illumination, the vehicle key alarm is intermittently activated, several attempts are required to start the vehicle, the engine shuts down unexpectedly.

Causes of fault code U0001:

  • The Control Area Network may have an open or short circuit
  • Damage to the CAN Bus harness
  • Low voltage due to a bad battery
Figure 2
  • Faulty control module
  • Control module has suffered a memory leak due to temporary power failure
  • The TIPM (Totally Integrated Power Module) may be defective
Figure 3

How Does TIPM Work?

Complicated-computer-circuits-electronics-type methods. Since it sends power to every electrical component in a vehicle, a non-functional TIPM can result in:

  • The vehicle not starting
  • Headlights not working
  • Brake lights not working
  • Fuel pump failure or burnout
  • Windshield wipers not working.

U0140 FORD Code – Lost Communication with Body Control Module

The Powertrain Control Module (PCM) continuously monitors Controller Area Network (CAN) for messages from Body Control Module (BCM). The Diagnostic Trouble Code U0140 sets when the PCM does not receive the BCM message within the defined amount of time.

U0121 – Lost Communication with Anti-Lock Brake System (ABS) Control Module

Symptoms of a U0121 engine code may include:

  • Malfunction Indicator Lamp (MIL) on
  • ABS indicator light on
  • Traction indicator light on (depending on manufacturer)
  • ESP/ESC indicator light on (depending on manufacturer)

Some of the causes for this code to set are:

  • Open in the CAN Bus + circuit
  • Open in the CAN Bus – circuit
  • Short to power in either CAN Bus circuit
  • Short to ground in either CAN Bus circuit

What are the Possible Causes of the U0155 FORD Code?

  • Communication error
  • Faulty Instrument Panel Cluster Control Module
  • Instrument Panel Cluster Control Module harness is open or shorted
  • Instrument Panel Cluster Control Module circuit poor electrical connection
Figure 4

Where to start?

So, there’s quite a few things happening here, it was time to do some research. After many road tests, and running the vehicle for a while, I eventually had a warning message displayed on the instrument cluster panel, ‘Accelerator action reduced,’ the check engine light and the ABS light came on, but the vehicle still performed well.

Pins 6 & 14 of the OBD connector were good, see Figure 1. The CAN Bus communication was good, see waveform in Figure 2. The CAN High voltage 2.62V, the CAN Low voltage was 2.31V.

After leaving the vehicle for two days and rechecking in the morning the vehicle would not crank or start.

Pins 6 & 14 of the OBD connector now gave a voltage of 122.7V, looking like one terminal resistor was not connected to the circuit, see Figure 3.

A Pico waveform at the connector pins confirmed something was not right, see Figure 4.

I decided to check the ABS module as the traction light control symbol appeared on the dash during the road test and the customer informed me that sometimes this symbol would appear while driving.

Time now to get a wiring diagram of the circuit (Figure 5)
to do some tests. The technical data showed eight different wiring systems for this vehicle. Therefore, it took some time to find the right wiring, by disconnecting the ABS multiplug and checking the wiring pins to match the correct wiring diagram on the technical data provided for this focus, what a pain!

I just could not reach enough behind the back of the battery tray and cover to disconnect the multiplug which was stuck solid to the ABS unit. Due to very poor access to the ABS computer I had to remove the battery and tray, air filter housing and a few other items to gain access for testing, then reconnected the battery – this went against my normal strategy for checking at the easiest point for access!


Figure 5: Technical data wiring diagram for the ABS system

The connector looked good with no corrosion or spread pins, see Figure 6.


Figure 6
Figure 7
Figure 8

I then checked the ABS computer lives and ground circuits before condemning the ABS computer. I load tested the two battery live pins 1 & 32, both red leads, and 1 ignition live pin 4 green and yellow, with battery support using a multimeter and test light, see Figure 7, which were good, 13.31V.

I load tested the 2 ground leads pins 47 & 16 black wires with reversed leads connections probing from battery positive to ground, being careful not to damage or spread the pins – these were good, reading 13.21V.

I was sure that the ABS module was the problem, but how incorrect I was – never assume. I get it wrong sometimes, I had to bite the bullet and move on! The (still poor) waveform with the ABS connector disconnected is shown in Figure 8.

Reflecting on my diagnostics, the next test had to be dictated by the results gained from my last testing method. I focussed my attention on the engine PCM computer as it was relatively easy to access the connectors, was near the battery and the ABS module that had just been tested.

I needed to check the PCM live and ground wires before condemning the engine PCM, as I have found faults with some of these systems before with poor supply and grounds issues. Time to find the technical data for this PCM, see Figure 9.

I load tested live wires pins F21,8,9,30 and M8 with the multimeter and test light, these were 13.2V. I then tested ground pins M5 and M42, F7and F40 with a multimeter and test light to load the circuits which were all black/yellow wires with reverse leads from battery live to ground 13.1V with battery support. The live wires and ground were all within specifications giving me enough evidence not to change the PCM.

The next easiest thing to check was the BCM. I disconnected the wiring connector and I still had a poor waveform indicating that the problem was not the BCM module. It was now time to get access to the instrument cluster and disconnect the connector at the rear of the display cluster. I did notice that the time clock display was reading incorrectly and made me think could the time clock lose the time display because it had lost the feed to it at some point? Or was this because of the previous garage testing and disconnecting the battery, or had the battery at some point become flat?

Observing the waveform on my PicoScope, after disconnecting the electrical connector plug on the back of the instrument cluster, the CAN signals returned to more normal display readings, indicating a fault with the instrument cluster module.

I sent the old unit off to be repaired and when it was returned, I did not need to reprogramme the instrument cluster or worry about any immobiliser or key problems that may be required on some systems, this can also be known as Proxi alignment.


Figure 9: Ford Focus PCM wiring diagram

I refitted the unit and this then fired the vehicle back to life and was starting every time I turned the ignition on to crank and start the engine. I rechecked the vehicle systems for codes and none were present and the vehicle was running again like it should.

In summary:

However complex the system maybe, test the components and systems in a logical step-by-step process, using the correct tools and equipment and provided you have access to the correct information you should be confident enough to solve the problem.

If you are not sure of your testing methods or your test results, try using other testing methods or test equipment and retrace your diagnostic test by backing up and then retesting your previous tests to get the results that you are happy with. Accessing the correct manufacturer data is very important if you are going to do a first-time fix, it’s not easy!

Plenty of patience is required and take time to rethink your strategies and plan of attack constantly.

Sometimes displayed symbols on the dashboard can mislead you into the wrong diagnostic testing procedures, we then need to step back, rethink and backtrack on our testing methods and retrace our steps.

This vehicle had kicked my butt a few times as every time it came into my workshop and I went to assess the circuit it would then start up before I could manage to take the test readings to find the fault.

I hate making mistakes, but I always learn from them and they help me to improve my diagnostic skills and development. You never stop learning, when you do, you die!

Some technicians tell me that vehicle courses are expensive, and yes, they can be! But they are no more expensive than getting the wrong diagnosis and then fitting expensive components that do not fix the vehicle. This is time- consuming and you end up in a worse position than you started out in.

Training is very important – it gives you confidence, knowledge and new skills to help you develop yourself.

About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
©
2024
Aftermarket Media Solutions Ltd, The Joiners Shop, Historic Dockyard Chatham, Kent ME4 4TZ
T: 01634 816 165
Company no. 09625886
linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram