Hi Folks, First time poster here.
My daughter owns a 2001 BJ Familia and it has an intermittent CEL.

We had the codes read and it was reporting a faulty coil (Coil B). Replaced both coils since I figured if one was worn out, the other may not be far behind. I should mention that the engine seems to be running fine even though the ECU thinks the coil is faulty.

Reset ECU and all was good for a few days then CEL again.

Read codes and reported both coils were faulty, Hmmmm.

Switched old coils back in, cleared ECU and all good for a few days then CEL again.

I'm about to take it back to get the codes read again but I'm thinking the fault is elsewhere and the ECU thinks it's the coils.
Has anyone experienced something like this before? Any Advice?

Thanks in advance.

Hi stevo99,

sorry no-one's got back to you so I'll put in my 2c worth:

Unfamiliar with the actual engine design but I'll infer from your post that there are 2 coils, A and B.

Taking the original coils to begin with: the ECU reported a fault on coil B. What you should do is if possible swap original coils A and B (mark them for ID):
- if the fault follows the coil, i.e. moves to ECU Coil A position, then the coil is at fault. Replace the coil.
- if the fault stays with ECU Coil B position, you know it's not the actual coil but e.g.the ECU, wiring harness, spark plug, something else.

With the replacement coils, assuming they were both replaced together:
- they may not be suitable/well built
- they may not be the right ones
- did you connect everything up again and/or properly?

Patrick

When replacing coils it's a good idea to replace the spark plugs as well, and the two (short) HT leads if they didn't come with the coils.
Mine's a 1.5 and has had 3 coils, yes both on one occasion and an odd one when the garage broke it taking it off too quick

I guess yours may be new enough to be a 1.6? The CEL had only just been introduced then (mine doesn't have one) and the on-board diagnostics are not as accurate as they should be. By which I mean it can give the wrong code.

From experience I can report that if you put it into a Mazda dealer they will replace the MAF sensor and charge you £250 (in the UK) and that may not fix the problem either!

As your BJ is almost as old as mine then it could be worth checking the air intake pipe (the one between the air filter and the throttle body, about 7 cms in diameter) because at that age they split, and let too much air in, so can cause EML issues.
With luck there's a picture of my old one on the way ...