O2 sensor plug

[karlandstace]

Can anyone enlighten me as to which of these wires does what?

Thanks in advance

[talkingcars]

Which model of car do you have?

[karlandstace]

Sorry. It's a 03 plate 160 vvc

[talkingcars]

F?
TF?

[karlandstace]

TF

[talkingcars]

Being a TF the answer is on the left hand side of page 25 of this guide from http://www.the-t-bar.com - http://www.the-t-bar.com/community/down ... l-diagrams

The brown/trace is a live and black/trace is a switched earth, probably the heater circuit and the other two are probably the sensor.
Do you have a picture of the other half of the plug?
IIRC the standard colour for lambda probes has two wires for the heater circuit as white, black and grey for the sensor.

[karlandstace]

Yes the sensor side is exactly that, 2 whites, one grey one black. So my suspicions would appear to be correct in that the plug is wired on to the sensor wrong. Nice one Rimmers! Payed over the odds for it as it was supposed to be OEM. Clearly not. Was Bosch not OE on these cars? The sensor I have is not a bosche.

Cheers

[karlandstace]

Great link by the way.

Thank you talkingcars

[talkingcars]

[karlandstace]

You see my problem.. So Rimmers tell me that the sensor plug in this picture is wired correctly (bottom plug). Meaning the plug on the loom is not. As you can see in this configuration the two greens from the loom are connecting to the black & grey of the sensor. Hence why I beleive its not working and throwing up a heater circuit malfunction.

I can not see why the plug on my car would be wrong. It's not been cut and looks totally original.

I'm getting very tempted now to simply cut the pug off my loom, re wire it so it leads to the sensor in the correct way and see if it works! Not sure what else I can do as Rimmers tell me all the sensors they have are the same and they have sold many without issue..

Any help or advice would be brilliant.

My plugs

[matgriff]

From what I can see, the wiring looks correct !!!!

In any case, what was the original failure mode of your first sensor ? unlikely that it failed with heater circuit malfunction, and the replacement sensor just turned up wired incorrectly and gave you the exact same fault

The plug on the sensor should be wired black/grey/white/white pins 1/2/3/4 respectively.

The green/yellow & green/brown are the switched signal output to the ECU. 0-1v to signal Lambda 1

The brown/pink is your live feed to the sensor, the blue/black is the switched connection from the ECU for the heater circuit. First check, is there 12v at the plug on the feed wire ?

Next, if you make a splice or temporary connection into the sensor, connect your multimeter to the heater circuit, +ve of the multimeter to the feed, -ve of the meter to the ECU switched output. The meter should read 12v when the ECU switches on the sensor heater (as the ECU output is an open collector transistor) if it reads zero, measure from chassis ground to the Blue/black switched wire, if that reads 12v, then either the wire between the ECU and connector is open circuit (unplug the ECU end and check continuity) or the ECU switched output has failed (unlikely) NOTE you must have the plug connected for this test..

Alternatively, just connect a resistor of about 20ohms 6W or so across the heater circuit and measure the volts drop across it.


Mat

[karlandstace]

Hi Mat,

Ok, about to give that a go. I'll let you know how I get on.. Good to know that my wiring is correct as I was about to start cutting and splicing!

Thanks for your help,

Cheers,

Karl

[matgriff]

OK feedback the results and I'll watch out for your post.

I highly suspect that you have a broken wire in the heater circuit, this is causing the ECU to correctly throw up the heater circuit malfunction error, and also as the 02 heater isn't actually working, the ECU won't go into closed loop fueling mode either, causing the running problems.

Have you connected an OBD2 sensor and looked at the live data ?

Mat

Mat

[karlandstace]

Hi Mat,

All test performed and it appears that the ECU switched output has indeed failed. I got 12v to feed but also 12v on the switched output wire when grounded to chassis. Continuity back to the plug was good.

I guessing it's a new ecu next then?.. Hopefully that will cure my problem!

Thanks for your help

Karl

[matgriff]

All test performed and it appears that the ECU switched output has indeed failed. I got 12v to feed but also 12v on the switched output wire when grounded to chassis. Continuity back to the plug was good.

I guessing it's a new ecu next then?.. Hopefully that will cure my problem!

Hi, just to be 100% sure... you get a 12v feed to the sensor on the pink/brown wire with the ignition on ? If you also measure 12v on the switched output wire at the plug (with everything connected) then that tells me that it's either the ECU output for the heater is "off" or the wire is open circuit, because basically the wire at the plug will be at the same potential as the feed (as it's connected through the 02 heater element)

if you ground the switched output wire to the chassis, you can't have 12v on it... it's grounded !

If you're measuring at the 02 sensor plug and it's 12v, then if you ground the wire at the ECU plug end, you should see the meter reading change to zero and the 02 heater will start to work, if it doesn't then the wire is open circuit somewhere.

Let me draw it out for you and it should make more sense

Mat

[karlandstace]

Hi Mat,

The more and more I think about it the more and more it confuses me! I'm not particularly electrically minded...

I performed the tests with the sensor connected as you advised but I don't really understand what the results mean.

Sorry if I sound thick!

Karl

[matgriff]

[matgriff]

OK here's the circuit... The ECU internally uses an "open collector " transistor to switch the 02 sensor heater,.. when the ECU output is off, then effectively there is no path for current to flow from the switched 12v live (shown at the top) to ground.

When the ECU switches it's output on, then it effectively connects the black/blue wire to ground, completing the circuit, current flows from the 12v live feed, through the heater, through the ECU transistor to ground.

If you measure from ground to the brown/pink wire, it should always read 12v when the ignition is on.. if you measure between ground and the blue/black wire... if the ECU output is off OR the wire between the 02 sensor plug is open circuit, you should measure 12v as well, as you're still measuring the same 12v feed through the resistor (it's open circuit so no volts drop across it)

If you physically ground the blue/black wire at the ecu end, you can't measure 12v on the same wire at the 02 plug unless the wire is broken somewhere in the loom (although you say you have continuity)

If what you say is correct, then indeed it could be the ECU, or at least something in the ECU control that's stopping the output for the 02 sensor heater coming on.... I don't know what that is though ?

[karlandstace]

Yes so with the -ve multimeter grounded to chassis I tested the brown/pink wire and with ignition on got 12v. I then performed the next test with the sensor connected and I still had 12v on the feed wire. I then tested the switch wire and I still had 12v. Obviously to me now, of course I would as the sensor is still connected at this point and completing the circuit.. So I need to do this test by cutting the wires rather than simply testing them in situ.

I think I have misunderstood your instructions and I need to test it again..

Karl

[matgriff]

You need to just make a temporary splice into the loom... if you unplug the sensor then you're removing the heater element from the circuit. Just make a scotch lock connection or similar..You need to be able to measure between ground, and the feed/switched wires independently with everything connected and in circuit.

basically if you measure 0v or a low voltage between ground and the blue/black wire with everything connected, then the ECU output and wiring must be OK and working...

One thing I don't know... if the ECU uses one output to switch both 02 sensor heaters on, then if one fails the total current would be half the normal value. The ECU would detect this, but it wouldn't be able to differentiate between the sensors (bank 1 sensor 1 or 2) have you double checked the other 02 sensor heater element ???