Oxygen Sensor Heater Circuit Question

[MUDGUTZ]

Hi, I have a Lexus GS 300 with P0135 & P0141 fault codes (O2 Sensor Heater Circuit Bank 1 Sensor 1 / 2)

I was thinking, before I go ahead and replace these, as it's only the heater circuit in each sensor that has failed (verified by fault codes and checked with a multimeter as open circuit), could I just join the heater circuit wires up to fool the ECU and clear the fault code?

I've heard about O2 Sensor resistance values of 12 Ohm, is this for the actual sensor or the heater? Even if that were the case, could I buy a 12 Ohm resistor from Maplin and put that in?

[eliot]

02 sensors dont work very well when cold, so the heater is used to get it up to temp whilst the engine warms.
It you bypassed it, it may clear the heater fault but you may get other o2 related errors because it will be giving out odd values.
Why not simply replace it - they are not that expensive?

[stevieturbo]

MUDGUTZ said:

Hi, I have a Lexus GS 300 with P0135 & P0141 fault codes (O2 Sensor Heater Circuit Bank 1 Sensor 1 / 2)

I was thinking, before I go ahead and replace these, as it's only the heater circuit in each sensor that has failed (verified by fault codes and checked with a multimeter as open circuit), could I just join the heater circuit wires up to fool the ECU and clear the fault code?

I've heard about O2 Sensor resistance values of 12 Ohm, is this for the actual sensor or the heater? Even if that were the case, could I buy a 12 Ohm resistor from Maplin and put that in?

So you're asking if you can short circuit a 12v and ground wire ?

Mmmmmm go for it.

Or maybe just fix the problem instead ?

[MUDGUTZ]

eliot said:

02 sensors dont work very well when cold, so the heater is used to get it up to temp whilst the engine warms.
It you bypassed it, it may clear the heater fault but you may get other o2 related errors because it will be giving out odd values.
Why not simply replace it - they are not that expensive?

stevieturbo said:

MUDGUTZ said:

Hi, I have a Lexus GS 300 with P0135 & P0141 fault codes (O2 Sensor Heater Circuit Bank 1 Sensor 1 / 2)

I was thinking, before I go ahead and replace these, as it's only the heater circuit in each sensor that has failed (verified by fault codes and checked with a multimeter as open circuit), could I just join the heater circuit wires up to fool the ECU and clear the fault code?

I've heard about O2 Sensor resistance values of 12 Ohm, is this for the actual sensor or the heater? Even if that were the case, could I buy a 12 Ohm resistor from Maplin and put that in?

So you're asking if you can short circuit a 12v and ground wire ?

Mmmmmm go for it.

Or maybe just fix the problem instead ?

Thanks for the advice.

In answer to the question of why not replace the sensors:

It's not a case of not wanting to, more a case of exploring different ways to get around this at a much lower cost.

I can't use generic sensors, apparently they don't offer the same resistance and can still produce a fault code.

£100+ for the two sensors is a reasonable estimate.

There are another two O2 sensors in the system.

I did find a little evidence on the web of folk using resistors to simulate the heater circuit, so it's not an un-tried concept.

Thanks again.

[eliot]

I find it slightly unusual that both heaters have failed,unless one failed ages ago and the other has now joined it.
The heaters are there for a reason - bypassing them is just being cheap - £100 for a pair isn't that bad in the scheme of car borkage.

[Steve_D]

Last o2 sensors I bought were £11 each.

Steve

[stevieturbo]

eliot said:

I find it slightly unusual that both heaters have failed,unless one failed ages ago and the other has now joined it.
The heaters are there for a reason - bypassing them is just being cheap - £100 for a pair isn't that bad in the scheme of car borkage.

Or it's a broken wire feeding both sensors.

Again, best to fix the problem, instead of bodging or guessing.

[MUDGUTZ]

stevieturbo said:

eliot said:

I find it slightly unusual that both heaters have failed,unless one failed ages ago and the other has now joined it.
The heaters are there for a reason - bypassing them is just being cheap - £100 for a pair isn't that bad in the scheme of car borkage.

Or it's a broken wire feeding both sensors.

Again, best to fix the problem, instead of bodging or guessing.

I've put a multimeter on both sensors on Bank 1: checking the wires that go to the heater circuit at the sensor plug (the ones that are the same colour) they both (both Sensors) indicate open circuit. If I were to put the multimeter on the socket, any ideas what the amps should be? Maybe that would rule out a break in the heater circuit wire that is common to both sensors. BTW I've received a quote from Lexus for replacement using Toyota sensors:

1 x Oxygen Sensor £160.33 + VAT
1 x Oxygen Sensor £153.10 + VAT

1.4 hours Labour @ £80.00 per hour £112.00 + VAT

Total £425.43 + VAT
Total Inc VAT £510.52

[stevieturbo]

MUDGUTZ said:

I've put a multimeter on both sensors on Bank 1: checking the wires that go to the heater circuit at the sensor plug (the ones that are the same colour) they both (both Sensors) indicate open circuit. If I were to put the multimeter on the socket, any ideas what the amps should be? Maybe that would rule out a break in the heater circuit wire that is common to both sensors. BTW I've received a quote from Lexus for replacement using Toyota sensors:

1 x Oxygen Sensor £160.33 + VAT
1 x Oxygen Sensor £153.10 + VAT

1.4 hours Labour @ £80.00 per hour £112.00 + VAT

Total £425.43 + VAT
Total Inc VAT £510.52

if you put them on the socket, there would be no amps, because that isnt what you would be measuring.

Clearly you need to check for 12v and ground. If you have a clamp meter or wish to connect an ammeter in-line with either of thsoe two wires, then yes you would hope to see current flow, but as the ecu is already telling you there is not and there is a fault with the heater circuit...not really a lot of point in doing that.

Likewise replacing sensors when the symptoms and information to hand isnt suggesting sensors are faulty...is a bit silly.

And whilst cheap aftermarket sensors are never great, £72 each is a tad cheaper

If you're able to unplug and poke at the sensor as you're already doing, changing them really shouldnt be too difficult that it would ever require a dealer.

http://www.ecolambda.co.uk/main/lexus.htm


But no point buying sensors until the fault has been diagnosed correctly.

[MUDGUTZ]

Thanks for the info stevieturbo.

I've had another check today and using the pins that are connected to the black wires on the sensors, they both indicate an open circuit, also this is the fault code I'm getting.

I'm going to try to change the sensors myself. I've ordered the special socket and a breaker bar and will first try to free the sensors then replace them one at a time.

It sounds like a PITA of a job but as access is good I'll give it a go myself. I much prefer to do my own work on the car, the standard of some garages is shocking and after emailing a couple of local guys in Northampton, it's obvious they can't be short of work.

One of the reasons I wanted to put it into a garage is the ball-ache of freeing the things off. I don't have any way of heating them like some folk do with an oxy-acetalyne torch.

[MUDGUTZ]

The sensor has arrived. Yesterday I gave the old one a quick tweek using the special socket and 45cm breaker bar and it came loose quite easily so I replaced it today.

The first thing I did with the new one (branded Walker, £72) was check the resistance of the heater circuit (pins connected to the black wires). It was 16 Ohm, so within spec as described by a poster on Lexus Owners Club

I checked again for codes, and they were both there, so I cleared them. Incidentally some fault code readers can set off the VSC & TRC lights on a Lexus. I found some info as below and cleared them also.

http://www.lexusowne...light/?p=837673

The new sensor came with some clips for the cable and a small sachet of copper grease. It was easy to fit.

I checked again for codes afterwards and they were BOTH gone but I would expect the code for O2 Heater Circuit Bank One, Sensor 2 (P0141) to come back on in the future, as I know that sensor heater circuit is open.

Thanks for your help guys.

[MUDGUTZ]

As predicted the EML came back on after about 30 miles. So I checked and the fault code for the heater circuit on bank 1, sensor 2 was there.

I've fitted the second sensor today. When I checked the resistance of this one it was 16.7 Ohm.

As before I checked and cleared the single fault code first and this time I don't expect it to come back.

Hope this thread is of use to someone who passes by looking for info.

The job is quite easy, provided you have the right tools.

Finally, shame on the local (Northampton & Daventry) garages who just couldn't be bothered to email me with a price for this job. Consequently I did it myself and proved how simple it is. They have lost income as a result.