Ford Focus ST: Case Study

Buying a car new or used will always be exciting. Sometimes though, when buying used, you may encounter symptoms further down the line, especially if the vehicle is older and has racked up some mileage.

This customer had purchased himself a 2010 Ford Focus ST, and after a few weeks of owning the vehicle, some symptoms appeared, so it was time to investigate.

Vehicle Symptoms:

• The vehicle will randomly not start. It can be ok for a week before not starting again.
• Immobilizer (PATS) light flashing when not starting
• If the vehicle does start, there are no other issues

Previous Work Carried Out:

• The instrument cluster has been reflowed as this is known as a top repair
• Dry solder joints were found and repaired successfully

An initial code scan showed these codes:

Usually, the instrument cluster would be looked at, however, this has already been fixed.

The two codes B112C and B2AE5 may provide us with more direction. The steering lock was also checked and it showed no issues. The door pull switch code was next to be investigated.

Passenger door pull switch 

Looking at live data with all doors closed, the driver's door was ‘off’ but the passenger door was ‘on’. Pulling the door handle on the driver's door changed the switch to ‘on’. This evidence suggests a faulty switch, but is this causing a random no-start?

While repeatedly pulling on the passenger door handle to see if the switch status changes, the scan tool loses communication with the Remote Keyless Entry module momentarily.

The same test was tried on the driver's door module, but this does not create a no communication issue.

As we can replicate the no communication with pulling the passenger door handle, clearing all the previous codes, and then creating a ‘no communication’ with the RKE created these codes. With the 'Theft Detected' code appearing, this switch looks very likely to be at fault.

Switch condition and location

Removing part of the door handle, some ‘stress’ was added to the switch body which kept creating the no communication issue. Stripdown of the door and removing the handle mounting to access the switch, reveals a switch that had internally corroded. A new switch was fitted, confirmed it is working in live data and since this, there were no issues with starting the vehicle, confirming a fix.