Engine Light Diagnostic Help - Berkshire - BMW Z4

Pre-Cat Lambda Sensor.

As above, could be corroded wiring. Pull the connector apart and have a butchers.

Probably will end up replacing it though, expect to pay 60-90 quid for a decent Bosch one.
 
And is the pre-cat lambda sensor something I could replace myself following a guide on the net? I have a limited amount of experience with cars, but consider myself capable enough to follow a pictorial guide.
 
In theory they are an absolute piece of cake. Unbolt old one, bolt new one in, Done.

Depending on the location of it though and access they can be a real PITA. Also they tend to rust themselves in being bolted into the hottest part of the exhaust. Various angled sockets and stuff are available to make things easier.

Best bet would be to have a look under the bonnet, find the exhaust manifold, remove the heatshield which should be easy enough and see what access you have to the sensor. The one you are after will be quite close to the engine before the CAT.

As for picture guides, I cannot find any for your engine but it isnt a complex job aslong as you can get a spanner on it!
 
The fault could be down to the circuit connections, the element in the sensor failing, or the wiring itself breaking down/shorting out.

I'm not sure if your car's ECU monitors the heater feed or the earth - it either expects to see 12v with the heater circuit activated or 0v if it is a pull down type where the earth is monitored. I'm fairly sure the heater elements are earthed at the sensor but the wiring may return (and earth) back at the ECU.

If you know this information then you can test the wiring at the plug by either shorting the 12v feed or using a jumper wire on the earth. The Ecu expects to see one or the other you see, so if you deliberately do the opposite of what it expects and you get a EML, this means good wiring :). This saves you having to strip back everything to the ECU

*warning* I don't recommend anyone to do this though! It is perfectly safe if you know what you're at but good potential for fried ECU.
 
MatteH Oxford said:
I wouldn't recommend that anyone reset fault code(s) etc unless the car has an obvious fault which they are confident of being able to fix.

The poor technician who has to try & fix the fault (when the vehicle owner almost inevitably gives up about 1 week later when the EML light comes on again) will have less evidence and information to go on to fix the issue. Sometimes the car needs to be driven multiple times to replicate the conditions in which the original code(s) was/were set & these may not occur *again before the vehicle is professionally examined. Especially when you have more than one issue, you may only get one error in the time before the technician sees the vehicle, yet originally they may have been 2 or more fault codes. The second issue may crop up until a later point after the vehicle has been 'fixed'.

This isn't a dig at anyone in particular btw. I wouldn't want anyone to pay more for expensive diagnosis time on a car than they have to, and resetting the eml/codes willy-nilly is likely to make people even more inconvenienced if not out of pocket.

Be careful! :)
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Fault history log.

kthxbai

[TW]Fox;23481198 said:
I think its probably unlikely that somebody popped round in the middle of the night and fixed his car without him realising though :p
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Ah thought he has no running differences, just the EML.
 
Very common for heater element in o2 sensor to fail, won't affect driving only start up when cold and EML light.

Change sensor for a oe or equivalent, do not use an aftermarket one.
 
pepsilol said:
Fault history log.
Click to expand...

:confused:

There is Kam (keep alive) memory in some ECUs which prevents certain trouble codes being erased by disconnecting the power supply but that is cleared by a proper scantool, leaving nothing to indicate previous fault codes if either the fault has been corrected or the conditions in which the fault codes are set haven't been met.

If you know something worth mentioning, then please go to the effort of explaining it properly instead of replying in a fashion normally encountered in GD. It isn't helpful
 
I think he's referring to the Shadow Fault memory in the M54's DME, which will show previously registered faults even after you've cleared the fault memory.
 
O.k. that would potentially be helpful but only if date/times for the codes are logged.
A list of every single fault code ever recorded isn't necessarily going to be much use!.
 
That's probably more helpful than a date/time tbh.

Cool feature, a shame it isn't part of more manufacturer ECUs. I'd still be cautious about resetting or clearing anything, even on a car with 'permanent' memory.
 
I agree, I'm not sure why everyone thinks resetting stuff and hoping it goes away is the right answer. Even the 'specialist' he went to did the same thing, what a suprise the light came back on. Cars rarely fix themselves!
 
I've done a little more digging because this has intrigued me, but ended up a little sidetracked by an article detailing how the Vanos system operates...

Apparently some "enduser" scantools (for want of a better phrase) are capable of clearing this shadow memory?:

http://wiki.bavariantechnic.com/ind...rian_Technic#Fault_Codes.2FShadow_Fault_Codes

Maybe or maybe not: selecting the option to clear all modules resets both ECU shadow memory using this scantool?. It seems to indicate this & the option to erase one type of memory or the other.

Fault Codes/Shadow Fault Codes

Fault codes, shadow fault codes, their descriptions, and fault status information are included in the display when supported by the control unit. The fault codes displayed are the same fault codes used by the factory tool. Bavarian Technic is different from generic OBD2 tools that only show emissions-related engine problems. When displaying fault codes, Bavarian Technic displays all faults and displays any additional fault information if it is available from the control unit.
To find additional information on faults, troubleshooting steps, and repair information, refer to the factory service manuals.

Erase Fault Codes/ Erase Shadow Fault Codes
To clear fault codes or shadow fault codes from the control unit’s memory, click on the Erase Fault Codes or Erase Shadow Fault Codes option, respectively, for the control unit selected. Alternatively, you can select to erase fault codes in all units at once by selecting the Functions menu option and clicking Clear faults in all units.

It is not possible to erase only one fault code. If faults remain after attempting to clear them, it indicates problems still exist. For example, if the fault code you see is “Seat belt buckle receptacle,” and you have not repaired the problem, you will not be able to clear the fault.
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[TW]Fox;23486747 said:
I agree, I'm not sure why everyone thinks resetting stuff and hoping it goes away is the right answer. Even the 'specialist' he went to did the same thing, what a suprise the light came back on. Cars rarely fix themselves!
Click to expand...

I guess it can depend on the type of car and how liable they are to throw a fault/light for a minor 'blip' rather than a full blown failure. Mine had the light appear, the code was a single instance of a lambda sensor fault. Reset the light and it has been fine for several months. (touch wood :p)
 
Kenai said:
I guess it can depend on the type of car and how liable they are to throw a fault/light for a minor 'blip' rather than a full blown failure. Mine had the light appear, the code was a single instance of a lambda sensor fault. Reset the light and it has been fine for several months. (touch wood :p)
Click to expand...

is it the golf in your sig? My TT had a lambda fault too. Cleared it in September and it hasn't come back. Checked voltage and the readings through vag com and they are all spot on!
 
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