We know that X300s can be a bit reluctant to set trouble codes and/or turn
on the CEL. On my car, "reluctance" is closer to outright refusal.

My misfire problem is getting worse but no misfire codes or
CEL. I've had several outright coil failures, and on many occasions have
disconnected coils, with no CEL or codes.

Crank sensor failure---no codes, no CEL.

Went for weeks with the air injection disconnected. No CEL or trouble code.

In experimenting recently I've disconnected the MAF and CTS several
times....and *left them* disconnected. Never got a MAF code and only once
got a CTS code. Even my arch nemesis "P0430" has popped up only once in the
last few weeks....after having been a regular visitor for years.

Now, I don't go around casting aspersions on ECUs as a rule of thumb. I'm
just not that type of person :-). However, I *am* beginning to wonder if
there is something fundamentally faulty with my ECU.

Thoughts?


Cheers
DD

 

I agree with you Doug, the ECU's are basically tough stuff.

What I am reading more and more on the X300 forum is fungus growing on/in the ECU connector plugs. Mainly damp climates like yours I think, and the UK.

Some say the sunroof drains, others the front screen seal/s, no matter, the dampness gets into the ECU sockets, as the plugs are facing upward. I have not heard of ECU getting flooded , just this awful growth at the terminals, and the cars have all run badly, and failed to run eventually.

A recent post here with snaps showed a bad one. "No voltage for the ignition....." is the title.

Might be worth a look see, it might be a simple fix, mmm.

 

Thanks, Grant.

Already checked my ECU pins a few weeks ago. Clean as a whistle

Cheers
DD

 

I am in the same boat as you are Doug. My CEL doesn't even light up when I turn my key. Yet half of my instrument cluster lights come on as well. For example my emergency brake light comes on when I turn on my car, yet when I set the parking brake I get no light on my dashboard.

 

Possibly a problem within the instrument cluster itself? In the case of the CEL perhaps even a burned out bulb?


Cheers
DD

 

my 95 xjr works the same way as Doug's, the only code to ever pop up was and is p0430. nothing else will trip the cel, not even bad coils.

 

Doug,
I had exactly the same lack of fault codes experience with mine when investigating intermittent starting problems over several months last year. Disconnecting several sensors that I thought would have certainly set fault codes did not and the CEL was never illuminated. These included, crank position sensor, cam position sensor, MAF, air and engine temperature sensors. Previously also I had no codes raised with faulty ignition coils. I would have thought that some sort of continuity or range check would have been performed at ignition on for key sensors and at least codes would be raised if out of limits even if the CEL is not illumunated. BTW my problem was an intermittent crank sensor. The car now starts every time since replacing it months ago and runs fine so I can only assume that this reluctance to set fault codes must be as normal as it gets for a Jaguar ECU.

 

Gents, thanks for the input. If nothing else it's good to know I'm not alone

I have to wonder if Jaguar intended this or if there's some sort of degradation or common fault that occurs with age. Like the solder joints on ABS circuit boards, perhaps?

Cheers
DD

 

I don't know, Doug. I would expect that the codes were generated from the same data as is used to operate the car and hardware should not affect how the software interprets the data. I do know that in my experience, the X-300 set plenty of codes during the time I had it. It might be thaty it takes a few start cycles for it to throw some of the sensor codes.

 

Didn't think of the key-cycle thing.

Other manufacturers, at least some of them, state in the service manual what the parameters for each trouble code are. Sometimes the window is quite narrow.

I would've expected outright disconnected components to be a "no brainer" for the system, though.

Well, anyway, back to chasing misfires. I just wanted to explore this "no CEL, no trouble code" angle a bit before getting any deeper. I think it's a little weird but probably not pertinent to the problem at hand.

Cheers and thanks
DD