BECM ECM shenanigans?

[AJV]

Howdy,

Having some issues with 2001 P38A (Bosch). Have recently had the battery out for an extended period troubleshooting alternator, charging, battery, parasitic draws. Outcome of that work is battery, alternator and draw seems all good (and have a good battery in there now)

However, when restarting the vehicle on several occasions it has kicked over but not started. On several other occasions I experienced an engine stop whilst idling (once in the middle of an intersection :) ).

Researched that it may be to do with the ECM/BECM handshake not occurring/losing sync. I note that to get the car going again I've been patiently waiting and manually unlocking and locking the car - as I understand that handshake between the ECM/BECM occurs with FOB/Manual unlock. So far this has gotten me going again (whether this is just good fortune or not however...) Car records error code Code P1668 - Anti Theft Alarm Serial Link Fault - Drive Cycle A

But I do wonder how it would be a ECM/BECM issue if the engine stops whilst idle. I don't know how the system works, but would have assumed handshake would occur at unlock - such that one might experience a crank but no start when starting the car (as I understand this is limited to non-GEMs), but not an engine stop whilst idling - the idea of the BECM/ECM software being written that engine immob would occur whilst the car is going seems crazy. Which leads me to think it may be the crankshaft position sensor, or something else in the engine (plugs etc).

Any tips or pathways to explore would be appreciated!

[prelude]

If you loose any of the sensors causing the engine stop it should register as an error so when you have the ability to read your engine codes that should show up. The only thing not registering in my experience is lack of fuel or "stalling" the engine, for sofar that is possibly with an automatic gearbox. (I had that with a faulty AICV that simply chocked the engine to death)

You should also try to erase error codes to make sure you are not confronted with errors that are no longer relevant. I do not know if the alarm/immobilizer works all the time, hence, can loose sync, but I do know there is an option in my faultmate to resync the two but that is only to fix the protocol I believe. Perhaps that would work as well? For as far as "decrypting" the ECU, it is certainly not just active when unlocking the car. The system also checks when there is a key in the ignition to see if that specific key is authorized to the BECM and that in turn checks with the ECU.

Mine -always- says the alarm is broken when I put the key into the ignition and I suspect a previous owner has simply had the BECM flashed or neutered so that the bloody system is simply bypassed, although, come to think of it, very occasionally when I try to start the car too quickly you can physically feel that you have the key on the start position but nothing happens for a second whilst the car is still determining if I am a thief :) and on even more rare occasions, it simply won't start at all and give me the error message on the dash. Simply removing the key and trying again more slowly always fixes that.

Good luck with the fault hunting!

Cheers,
-P

[PeterH]

I have same model as yours, 2001 P38A Bosch.
I was driving home from work one day, in peak hour traffic, just as I was entering a major roundabout, the engine died with no warning.
It would turn over no problem, but just wouldn't fire.
No error codes on the message centre.
After 15 mins of trying to problem solve, I had at least a kilometer of traffic built up behind me, when a great guy in a disco pulled up and towed me through the roundabout and out of the way of the traffic.
I got a tow truck back to my driveway at home, where I could have a proper look at it.
You should have seen my face when it turned over and started straight away! Good grief!
It turned out to be the Crank Position Sensor, once it had cooled down it started working again.
When they start playing up they are a show stopper.
I got a new one and I was back on the road in under 24 hrs, never had a problem with it since.
I would change your CPS first, you might find that solves the problem, or at very least you know that part is good.
I'd do that before diving deeper into other things, plus it will probably save you from future breakdowns due to a faulty CPS.
Hope that helps.

[AJV]

Thanks for the considered replies!

Will pursue a new sensor being an easier intervention to test over the next few weeks and update this thread.

AJ

[redandy3575]

Very similar situation. My wife drove my kid to school, went to start up, engine fired up, but was running very rough. Then latter just wouldn’t fire up at all. Engine cranks over, but to no avail. Will be interesting to see which sensor is playing up, the crank position sensor, or crank angle sensor.

[AJV]

Been a little while. But as an update and to close this one off for the benefit of all determined p38 owners :bat: - it was the crank angle sensor that was on the fritz.

A new one cured it. Thanks all for the posts