850 Est 2.0L 20V 1996 Engine Management info needed.

Ricky_devon · Post by **Ricky_devon** » 22 Jan 2010, 13:11

Hi all,

I continue to have problems with my car engine managment system.
Just pre christmas, it started to play up, intially replacing the battery seemed to solve it, but soon the faults returned. I am not going to go into detail of the 'story' so far as it is too long! I have got to the point that having had the dianostics plugged into several times, codes read & cleared, replaced the Lambda sensor - which has improved things - and the MAF sensor - which is still questionable - may have a dud one. I need to know what voltages should be at the 4 connection points at the MAF sensor, so I can determine if I have a faulty ECU or MAF sensor. Does anyone have this info, or an idea where I can find out?

Thanks.

Post by **Ozark Lee** » 22 Jan 2010, 14:10

What were the code numbers when you had the car scanned?

...Lee

Ricky_devon · Post by **Ricky_devon** » 23 Jan 2010, 06:40

Hi Lee,

Hopefully will see the mechanic dealing with later today & find out.

Ricky

Post by **Ozark Lee** » 23 Jan 2010, 06:54

While you are at the shop with a scan / reset tool have them just unplug the MAF sensor and see how it behaves. It will set another code but if the idle smooths out then your replacement MAF sensor is likely bad. The plus in doing that test there is you are at the shop and the code that unplugging it will set can be cleared on the spot.

...Lee

Ricky_devon · Post by **Ricky_devon** » 23 Jan 2010, 16:19

Hi Lee and all,

Unfortuantely I missed the guy at his workshop today - he was out attending a breakdown, I've already left the car with him since it was virtually undrivible - I'd only go with it with someone else following to tow if needed, although it make to his place unaided! So keys locked in his garage, I have since spoken to him on the phone.

Although it has the newer type of diagnostic socket - in the car under the coin tray, I'm quite surprised to learn that it still gives the same format of codes as the older system with the flashing diodes in the engine bay.

When he first plugged in, all sorts of codes came up, I can't remember them all, but included on the list was lambda sensor, loom faults, maf sensor, low fuel pressure. Clearing the codes resulted in the lambda code coming back first every time, so while wondering if infact it is a faulty ecu as so many parts can't have failed all at once, he replaced the lambda sensor. After this, and clearing codes again, all codes stopped except MAF sensor code. The code comes back after every clear down. I had replaced the MAF sensor, before the codes were read, after advice from a 3rd party, however it is a non OEM from ebay, so is not beyond question that the new one maybe a dud.

The code given is 121.
According to the UK Autodata book, this translates as MAF sensor/loom fault. System type = Bosche Jetronic LH 3.2.

Engine model (read from the cam belt cover) = B5204S.

So, if we could find out what the voltage at each one of the MAF Sensor connector (4 pin) should be, we could isolate whether;
1- correct signal coming from ecu?
2- correct feed being returned from the MAF sensor?
Also - is one a earth/ground?
Therefore; if it is the MAF sensor, or a loom/ecu fault.
The guy has a pin autodata manual, but it only goes back as far as version T, not S as mine is, and of course he can't be sure if a change was made between the two different types.

The only other thing to note is that having read so many posts, compared to others, it would seem unusal that my temp guage rarely makes it above 1/4 on the scale - except very hot weather/stationary traffic, occasionally the gauge fails to read. This is not a recent development though, been like this since I've had the car. Faulty coolant sensor??

Hope that someone can advise.

Ricky.

Post by **jblackburn** » 23 Jan 2010, 16:47

The only other thing to note is that having read so many posts, compared to others, it would seem unusal that my temp guage rarely makes it above 1/4 on the scale - except very hot weather/stationary traffic, occasionally the gauge fails to read. This is not a recent development though, been like this since I've had the car. Faulty coolant sensor??

Bad thermostat. They tend to take the coolant sensor with them, so replace that as well.

That said, I don't know what numbers the MAF is supposed to be reading (I'm not sure it will read anything by itself totally unplugged so I'm not sure there's a way to test it), especially on that engine, but if it runs better with it unplugged, then it is very likely that the new one is bad. For the pin layouts, I would think 1 is power, 1 is ground, and the other 2 output some kind of voltage feedback to the ECU computer. The cars are particularly picky if you use an aftermarket brand sensor on them.

Post by **jblackburn** » 23 Jan 2010, 16:55

However, here is a table of the voltages you should be getting at the ECU itself. Look at the voltages at A13 on your model (this ECU configuration is MUCH different than my S70's, as are the voltages from said sensor - wow!)

Looking at this, it looks like maybe unless you buy the MAF specificially made for your car, it may be putting out much lower voltages (as for the other 850 models) that your car doesn't know what to do with. According to this, you'll be seeing between 2.9-3.6V, instead of the .9 or something my S70 should be relaying back to the computer.

I hope I got the right engine here.

Ricky_devon · Post by **Ricky_devon** » 24 Jan 2010, 05:40

Hi,

Thanks for the ecu voltage table, we should be able to use this.

Ricky.