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Accessing PCM/ECU connectors

Posted: Thu Apr 27, 2017 11:06 am
by warpc0il
When fault-finding electrical problems you are quite likely to come across references to "the PCM connectors" - especially as (nearly) all the vehicle systems talk to the Powertrain Control Module - sometimes referred to as the ECU (Engine Control Unit), even though modern PCMs control much more that just the engine.

The PCM is located behind the offside headlight under a black plastic cover.
PCM.jpg
PCM.jpg (70.79 KiB) Viewed 2043 times
To check the PCM connectors properly you really need to remove the PCM itself - a very easy job on all but UK-spec cars.

In order to meet Thatcham Security requirements, and therefore keep the car in a sensible insurance group, Mazda were required to fit tamper-proof bolts holding the PCM. The heads of these bolts shear off when tightened, leaving just a dome. In some cases it's possible to remove one or two with Mole grips but you'll almost certainly have to drill the rest out. Unless you car has had its PCM/ECU remapped, in which case someone else would have already done this and (hopefully) replaced with normal bolts.

Even the very early (pre-certification) cars that don't have the shield on the back of the OS rear light, still have the security bolts fitted, as the Ford guys gave Mazda the heads-up on the generic requirements.

I used a left-handed drill bit (yes they really exist) as I've had some success with the bit digging into the head of the bolt and spinning it out, without having the drill the whole thing off.

If you have to drill them out you/ll need a selection of short M5 and M6 socket head bolts to resecure it.