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ECU fault

6K views 28 replies 12 participants last post by  MG-Lewis 
#1 ·
Hi all,
As the thread might suggest, I am currently experiencing a probable ECU fault on my TF LE500.

So in summary:
Ten days ago, engine management light comes on. Quick consultation with the manual says it's not flashing so I can carry on driving but probably should book a service.
One week ago, my mechanic friend runs diagnostic. His machine is older (his business is a start up), so we get generic codes. He doesn't think it's too much to worry about though, and suggests that we reset the codes and see what happens.
As you can probably guess, the light came back, so today I went back to him for further investigation. One code repeats from last week and it relates to the ECU. Alongside this are a number of other codes - because they differed from last weeks codes, he decided before anything else he would check the wiring. This is where I leave him to it.

So next thing I know, the alarm is going off, but this is now looking like an ECU snag rather than wiring as it carries on even with the battery disconnected, and he can't get the key fob to unlock it. ECUs are not his strong point, nor are MGs, but we have a mutual agreement - mates rates for cash flow (as I mentioned, start up business), so I've taken my car to him a lot for minor snags.

In short, I left his workshop today without my car, with the alarm still going and (increasingly likely looking) worst case scenario, a buggered ECU, and I kid you not, I was bawling like a baby (much to his discomfort and distress), because she is my absolute pride and joy. Short term, I've hired a car and he's going to continue to investigate the wiring just in case. Long term... I am desperate to not have to give up my baby, but I am frankly terrified at the prospect of having to fork out for a new ECU (plus associated costs), so any hints and tricks would be very greatly appreciated!

Thanks in advance
Sian
 
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#3 ·
Alternator belt recently changed (by the mechanic friend so if he hasn't already he's certainly planning to go back and check everything in the vicinity) and battery is less than a year old, so on the face of it at least, should be no issue there
 
#4 ·
What codes did you get then?
 
#5 ·
It was something like P0161 for the recurring one - definitely relates to ECU but his machine gave quite a generic description (it officially reads up to '05, seems it can get codes for my '09 but not always good or accurate descriptions without help from google). Real mishmash of other errors, and different ones after each reset. Couldn't tell you all of them off the top if my head but he may have noted down some. Got P0535 twice as well but don't want to fixate on the other codes as they've not been consistent
 
#6 ·
The only connection between the alarm and the ECU is that the alarm tells the ECU it is okay to start the engine (i.e. disconnect the immobiliser).

To be of any help we really need to know the codes. The engine management light only comes on if there is an OBD fault although the system holds other fault codes.

James
 
#7 ·
Charge the battery. A friend of mine had a problem with his alarm on a LE500 when the battery went flat. The alarm has an internal battery and he could not get it to stop once it started going off. Once he had a charged battery all reset back to normal. The alarm on the LE500 is controlled by the BCU, as it is in later MG Rover cars.
 
#8 ·
Almost got the code right, it was P0601 which is recurring. Also P0535 has come up more than once.
In addition, yesterday we got P0032, and previously P025d. I am assured the alternator is fine. He'll check the battery voltage, but I'm confident myself that this isn't a battery thing - I've had my fair share of those, believe me, with this one and my previous!
 
#9 ·
PO601 indicates that the self diagnosis checksum test within the engine ECU is failing - in other words, the ECU is not performing its calculations as it should (this can then effect fuelling and emission, as well as power output and performance). If the car battery is good and the alternator charging properly, and all wiring and connectors are good, the usual solution would be to replace the ECU with another unit.

PO535 is I think a fault with the air conditioning sensor - possibly the sensor itself, or maybe damaged wiring. I seem to think this code has sometimes appeared as a 'ghost code' on other MG Rover cars which are not actually fitted with air con.

PO032 is a fault with a lambda sensor - again possibly a faulty O2 sensor, or possibly damaged wiring/insecure connector.

Is the other code you have given correct??? - there is no code ending with a letter to the best of my knowledge; all OBD codes are a letter followed by four numbers.
 
#10 ·
According to my records the Fault Codes are:-
P0601 - Control Module
P025? - Injection Pump (I think this may refer to diesel)
P0032 - Heater Control Circuit (could be temperature sensor failure leading to overfueling)
P0535 - Not shown but is in the area referring to air conditioning faults.

I appreciate that your Mechanic is a friend, but if he does not have the proper test equipment to hand maybe it is time to get in someone who does so that the fault can be properly diagnosed. It may save the friendship in the long run.

Mike
 
#12 ·
Ooops!
Minor cock up, P0032 is O2 sensor heater circuit fault (I obviously didn't read the title properly).
The O2 heater is usually only useful at start up to prevent overfueling, once the exhaust manifold is heated up the sensor should work without the necessity of the heater circuit.
I would think that this is a symptom rather than the cause of the problem.

Mike
 
#11 ·
He has actually said as much himself, Mike. Unfortunately the car is currently stranded due to previously mentioned issue that the alarm/immobiliser has managed to jam itself on.
It is also around 50 miles to the nearest MG main dealer (although I believe there is an MG Rover guy a bit closer to home) - fine if I could start the engine as this is where it goes for regular servicing (minor jobs have been going to my friend just to help the new business), but...

Well the car has air con and I have recently had an odd noise which I think was coming from the approximate area of the air conditioning 'gubbins' by the glove box, so errors in this area actually wouldn't surprise me (and before anyone says anything, I tried to get that noise checked, but it has been intermittent so naturally goes away as soon as anyone qualified gets in the car, then comes back 5 minutes after I leave them)!

Thanks both for the fault code info, will pass it on - if he can at least get it to a state where it will start, if I still have errors and the sensors 'Man in the Car' has suggested seem OK... As you say, time to pass on the problem to someone with the kit!
 
#18 ·
As above worth checking your battery, some TF components only activate (power steering, ABS, etc) if the battery has enough cranking power (cca).

The TF requires around 600 cca. (cold cranking amps)

Batteries can also give false readings if there on their way out, they can show fully charged at around 12.8v but not have enough cca to start the car and will die when you turn the key.
 
#19 ·
As you are getting exactly the same symptom on the same model of car that my mate has and his alarm going off and continuing even when the car battery was disconnected was solved by fitting a fully charged battery, I still think that ensuring the battery is fully charged should be the first thing that you try to resolve that issue.
I am not suggesting that it will cure all of the problems and stop all fault conditions recurring, but it is very cheap and easy and may make more of a difference than you think.
 
#21 ·
Hi all, sorry I've gone quiet... Had a crazy busy two weeks, big birthday in the family followed by a very 90's hen do two days before the wedding, the result of which was I've only spent two days at home since my last post.

So lambda sensors look to be an actual fault rather than a potentially false one... Quoting my mates question so he can check the sensors before fitting.... "Could someone please range the good ohm readings for the lambda heater circuit, and confirm that at 2500-3000rpm I should be seeing 0.98-1.02v on signal wires."

I'm feeling a bit happier having been loaned my parents B for a couple of weeks ;) but still would quite like to get my car back!
 
#22 ·
the lambda sensor will require replacement as the heater element has failed , ( now has to wait for car to warm up and will cool at idle causing fueling errors , high emissions etc ),
readings from said sensor will be from 0 volts to 1 volt depending how he is checking it (0-0.4 volts =lean mixture under fueling , 0.5 - 1 volt = over fueling ) , with it still installed in the car it would have to be run up to temp and checked and ideally would give a reading of 4.5volts if all fueling etc is correct (which i doubt because the heated elements isn't working ).
 
#24 ·
Seem to have misunderstood things myself, he wants to confirm the fault before forking out for sensors. So needs the expected ohm reading on a good sensor (as per my above question) rather than the volts in order to test them... If this proves to be a definite snag, then he will order and replace. Otherwise... Well, who knows. But at least we have something to come back to and check if the light comes back on!
 
#25 ·
cant give a definite voltage as if the heater element has gone it will be different at different temperatures as fueling will be altered and the sensor will not be working as intended.
if he has a code reader he should get the code for o2 sensor heated element not working , if he is in doubt tell him clear the codes and turn ignition off and back on again and re read the codes to see if it is the same code .
 
#29 ·
Many thanks, that is what we were after. This has confirmed it was a bad sensor and not a spurious reading. Do you know what would have been originally fitted (oem) as it seems it had a replacement already and we suspect (/hope) this might be contributing to the the p0601 code.. It's bank 1 sensor 1 (pre cat) lambda sensor. There is a good chance is will have been specific to the LE500 and different from the TF (increasingly seems to be the story of my life)!
Thanks in advance
 
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