How to use the On-Board Diagnostic (OBD) unit.

[billofdurham]

The 400 series, with some exceptions, was fitted with an On-Board Diagnostic (OBD) unit from the 1990 model year. The unit is located in the engine compartment and allows the owner to read Diagnostic Trouble Codes (DTC), more commonly called fault codes, which have been stored.

The attachment contains the instructions for its use.

400 OBD.pdf

(934 KiB) Downloaded 1248 times

Bill.

[cornish4475]

Hi there,

You say that the obd isn't fitted to 1.7 petrol turbo's, but my '95 glt turbo auto's got one.

Haven't tried it out yet though, but i will do and let you know if you like?

ps either way, very good article thanks for posting it.

Rob

[billofdurham]

That is very interesting as my programme blanks out the OBD section when I select the 1.7 turbo model.

If you do try it I shall be very interested in the results.

Bill.

[cornish4475]

I have tried the obd out and with reference my post rough idle, high emissions, low mpg it did indeed work and came back with one fault code: 113 (injector wiring open circuit).

Bill, this makes sense to me as the problems i'm having would be associated with a faulty injector circuit. Do you think?
Maybe your system doesn't register turbo's as i believe they have two ecu's, guessing at one for spark and one for fuelling, so the "extra" ecu would possibly be the spark one as the fuel circuits are obviously connected to the obd, hence my fault code. If the fault codes mean the same thing on turbo models that is! Of course i could be completely wrong on this.
So it appears when i have some daylight i'll be hunched over the injector rail with the circuit tester, whatever my results i'll be posting them but i hope it is this simple!
Rob.

[billofdurham]

Thank you for that, Rob.

The codes do mean the same for turbo and non-turbo but the turbo usually has more codes.

It is only the 4 series that blocks out the codes for the turbo models on my programme. Every other turbo, including non-Volvo shows them.

The resistance range you are looking for at 20C should be 14 to 17 ohms.

Bill.

[cornish4475]

Thank you Bill,

Slightly confused though, you say resistance should be 14 to 17 ohms, the pdf you posted some time ago ref fault code 113 says 1.1 to 1.5. Or did i write it down wrong?
Rob

[billofdurham]

You wrote it down right but that was for a single point injection system on a 460 1.8.

Bill.

[cornish4475]

Hello again,
I disconnected the wiring plugs from the injectors and measured the resistances. The wiring plugs were either 14.1 or 14.2, the injectors themselves were all 16.1.
It was a little colder than 20C though. Is the anything else i could try?
Many Thanks.
Rob

[billofdurham]

The values are close enough.

The only other thing to check is the signal to the injectors.

Ignition OFF.
Disconnect the injector plugs.
Connect a LED test lamp to each of the plugs in turn.
Briefly crank the engine.
Check that the LED flashes.
If the LED doesn't flash check the wiring.
If the LED flashes there is a possible fault in the injector.

Bill.

[cornish4475]

Thanks Bill,

I'm totally self taught so can i clarify please?
You suggest using a led test lamp, is this because an led will only light at a pre determined voltage and an ordinary bulb will light at a lower voltage?
I take it i can't use my circuit tester as it won't be able to keep up with the "pulses"?
Would any 12v led bulb and some lengths of wire do?
Sorry to be a pain and thanks again, Rob