Motor Vehicle Maintenance & Repair Asked by lericson on March 19, 2021
Car: Ford Focus Mk II 2010 Diesel TDCI 1.6L
When I push either turn signal, it lights up the appropriate light on the dashboard and flashes the corresponding turn signal VERY briefly — about a tenth of a second, and then it clicks off. No matter how many times I push the lever, it does exactly the same thing.
The same behavior arises with the hazard lights, but if I do it three or four times, it’ll actually start blinking properly. When it fails, either left or right will blink on its own very briefly.
Note that the turn signal switches off in the dashboard too.
As far as I can tell, nothing else is acting up. Heaters, radio, windshield wipers, etc all work as before.
Please, how do I diagnose this bizarre behavior? There are no DTCs.
I should note that this happened shortly after I programmed a new additional key.
I fixed my problem by finding a circuit diagram of the entire car, or at least a very similar model.
It turned out the flashers, blinkers -- or their technical name, the turn signals, are controlled by a microcomputer in the fuse box at the passenger's side footwell. The technical name is the PJB, or "passenger junction box", it's basically the fuse box for everything not related to the engine.
I tested the turn signal switch with a voltmeter, and there was nothing wrong. By my symptoms, it seemed unlikely to be a grounding issue too -- but nevertheless I provided an alternative ground to the PJB, and still no dice.
So, I figured it must be something wrong with the PCB. Modern electronics do have a shelf life, mainly because of the capacitors -- they dry out and lose capacitance. Capacitors are also commonly used to drive timing chips...
Anyway, long story short: I replaced the PJB with a junkyard one, and it works fine.
Correct answer by lericson on March 19, 2021
Hazard lights and blinkers are controlled via ECU outputs into a module called a FLASHER RELAY , if this relay fails then you will not get flashing (Can you manually index the flasher to simulate flashing(repeated on and off of the signal stalk).
You can try to reset the ECU by removing the battery cables for a period of time and reconnect them, otherwise you might need to replace the flasher relay and or flash module.
Answered by binaryOps20 on March 19, 2021
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