A guide to reading fault codes on your 1990-1993 240
 

For those of us who have a late 240, specifically those made from 1990-1993 fitted with Bosch LH-Jetronic 2.4 fuel injection, I'm sure we've all seen and experienced the horrors of the lambda light. What this light actually means is that one of the engine computers has detected a fault somewhere in the engine management system and is alerting you to its presence BEFORE any damage is done as a result. This post will explain how to use the self-diagnostic function to read codes and diagnose problems indicated by the lambda light.

TERMINOLOGY:
ECU: the Engine Control Unit, which is a computer located on the right of the driver's side footwell. this computer controls fuel delivery to the engine.
EZK: a smaller ECU located on the passenger side firewall that controls spark timing for the engine.

Right, so you've go the dreaded lambda light illuminated on your dash. The car may seem to be running fine, it may be running rough. No matter, the light is telling you the ECU or EZK has detected a fault. What we're going to do is find out what the computers think is wrong. The first step is to open the bonnet:

http://i.imgur.com/JlMjAl.jpg

The arrow points to the diagnostic box. If you take a closer look, it looks like this:

http://i.imgur.com/lxHwel.jpg

Pull the lid off the box, and you're presented with six sockets, a diagnostic probe, an LED and a button:

http://i.imgur.com/y6I1El.jpg

With the ignition turned off, insert the probe into socket 2 (to read codes from the fuel ECU) or socket 6 (to read codes from the EZK). Turn the ignition to key position 2 without starting the engine. Press down the button on the diagnostic box for about 2 seconds, and the LED on the box should flash out a three-digit code, i.e 3 flashes, space, 2 flashes, space, 1 flash would be code 3-2-1. After reading the code, depress the button again for 2 seconds to see if further codes are stored. If the same code repeats, there are no further fault codes stored.

It is also worth noting that not all fault codes cause the lambda light to illuminate. If you're having running difficulties, it's worth checking to see if there are any stored codes which could point you the right way.

Below is a list of all the fault codes that can be stored:

ECU:
1-1-1 - No faults
1-1-2 - ECU internal fault
1-1-3 - Lambda control - engine running too rich/lean
1-2-1 - Mass air flow meter signal faulty or missing
1-2-2 - Air temperature sensor signal faulty or missing
1-2-3 - Coolant temperature sensor signal missing or faulty
1-3-1 - RPM signal from EZK missing
1-3-2 - Battery voltage too low or high
1-3-3 - Throttle position sensor idle setting faulty
1-5-4 - Exhaust Gas Recirculation flow too high
2-1-2 - 02 (lambda) sensor signal missing or faulty
2-1-3 - Throttle position sensor full load setting faulty
2-2-1 - Lambda control - engine running too lean at part load
2-2-2 - Main relay faut
2-2-3 - Idle Air Control valve signal missing
2-3-1 - Lambda control - too lean or too rich at part load
2-3-2 - Lambda control - too lean or too rich at idle
2-3-3 - Idle air flow outside control range
3-1-1 - Speedometer signal to ECU missing
3-1-2 - Knock sensor signal (from EZK) missing
3-2-1 - Cold start injector signal missing or faulty
3-2-2 - Mass Air Flow sensor burn-off signal missing or faulty (MAF wiring fault)
3-4-4 - Exhaust Gas Recirculation temperature signal missing or faulty

EZK
1-1-1 - No faults
1-4-2 - EZK internal fault
1-4-3 - Knock sensor signal missing or faulty
1-4-4 - Load signal from ECU missing
2-1-4 - RPM sensor signal intermittently missing
2-2-4 - Coolant temperature sensor signal missing or faulty
2-3-4 - Throttle position sensor idle signal faulty

Once you've repaired the problem or to check if the problem is still present after repairs, you'll need to clear the codes from the ECU/EZK. This is accomplished by inserting the probe into the appropriate socket and read the codes as detailed above. Once the codes have read themselves out, press the button for more than 5 seconds. After 3 seconds, the LED should light. Press the button again for more than 5 seconds. the codes should now be erased. You can then repeat the procedure for reading codes and you should read '1-1-1' for 'no faults stored'.

I hope this post is useful and keeps everybody on the road! If anybody's got any additions or amendments to what I've written, don't hesitate to contact me or post them up.

Edit: Link to original thread

Thanks for that very useful fact sheet.

Mike

Great:thumbs_up: Thanks for this one Wooble, I'll ask for it to be moved into the articles section .

I have had two cars where the standard way of clearing the codes did not work. The sure way is simply to disconnect the battery for a second or two. (But it may lose radio memory settings)

Your description is a lot clearer than J.H.Haynes, wooble!
Thanks for taking the time to set it out clearly.

Worth printing out and keeping in the car.

Well I stumbled across this old post while looking for a non running issue on a K reg 240.Very useful stuff and ought to be in the "ARTICLES" section.

Any chance it could be moved dear kind admin?
Regards Brian.;)

Looks like I said I'd ask for it to be moved in post#3 Brian.... must have failed. Anyhow it will hopefully 'make the move soon':thumbs_up:
Thanks for pulling it back up again:thumbs_up:

I didn't notice it was an old article, and I had already commented on it :)


But I would add that the light can be triggered by a momentary fault or a passing glitch. It doesn't necessarily mean there is still a fault to be found.

I once went over a shower of pebbles on a gravel car park. One must have hit the engine block hard enough to trigger the knock sensor. The lambda light came on and the engine felt a bit odd. I guessed what had happened and cancelled the codes, and it was then fine.

In my experience it's always worth noting the codes, then just resetting and seeing what happens, before getting too worried about tracing faults that aren't real.

^^ As he says