I have a Peugeot 206 1.4 on a 2006 plate KFW engine which doesn't charge properly. Originally when I drove the car it was fine but then on a wet dark night the battery light came on. I switched the ignition off and the car wouldn't start. After 5 minutes it kicked back into life and off we went with no light on. We did a quick check and out a new alternator and battery on it.
At idle the alternator charges at 14.2 volts but when you switch everything on it drops to 12.2 volts. We've checked the earth cables and done some volt drop tests but the only issue we've found is with the control wire that goes from the alternator to the ECU this is a PWM signal which at full load on the vehicle should drop to 0 volts, but it doesn't it actually sits at 1 volt. I've included some scope patterns taken from the vehicle. I've used a four channel scope and looked at the following;
Battery voltage (Blue)
Control from the ECU to pin 2 on the alternator (Red)
Exciter wire from the BSI, this wire is also used to bring the warning light on (Green)
Current draw (Yellow)
I was lucky to have another 1.4 206 in the workshop so could scope that at the same time. The red pattern on one drops from 12 volts down to 0 volts. The other sits at 15 volts and drops to 1 volt. Why is this and where is that 1 volt likely to be from. I would use a wiring diagram but the Peugeot diagram shows it going to pin C4 on the black ECU plug. But that has no wire going to it. Any help would be great. Thanks Pete
Hello that's what concerns me in the first capture the voltage never drops below 1V - on the good pattern it drops all the way to 0V.
The ground is direct to battery with a good connection. We also checked for a volt drop at the battery connections.
Will change the sample rate and time base when I get the chance to scope it tomorrow.
Will put a load on the system and scope again. Driven the car again this evening with heavy rain, so had the wipers, rear screen, air con, lights and fan on setting 4. No warning lights came on.
Blue - Battery voltage at the battery + and - negative terminals
Red - Control from the engine ECU to the alternator
Green - Current from the BSI to the alternator to excite it.
Yellow - Current reading taken from the positive wire at the battery
Volt drop on the Alt + to Battery + is 0.01v. Hope this makes sense Peter
Thank you for the continued posts and the psdata files, these are great for all to see.
Here we then have your vehicle performing as expected with no fault (Which I know is always the way)
Alternator output relative to load is good and the exciter circuit remains stable throughout.
It still begs the question as to why the control signal voltage level is greater than battery voltage and this must tie in with the ground that appears to float around 1 V (Channel B)
I would concentrate on this circuit and the component responsible for generating this control signal
How is this component grounded and what route does the ground take before termination at the chassis?
Thank you once again for the continued posts, any feedback would be most valuable as you continue to use this vehicle
Come to think of it, as its your vehicle, would it be possible to monitor this signal with your scope during various journeys looking for characteristic changes in battery voltage (use OBD pin) and control signal voltage.
I don't know if this will help in your diagnostic process.
I found a document which describes some of the problems you are struggling with in terms of the 1 volt offset, but it doesn't give any solution to this problem, other than to test a known good alternator.