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P1135 Fault Code


rpaterson
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Hi folks.

I've had an intermittent engine light for ages and had just assumed that it was one of the O2 sensors. It's been on constantly for a few weeks now but I got a code reader for Xmas so I tried it out yesterday and it displayed the P1135 code which we all know refers to the O2 sensor. My question is, is it definately the heater circuit that this refers to? Also, if it does-can I just splice into the loom of the other 'good' heater circuit to put the light out rather than spending 150 quid on a new sensor?

What does the heater do, does it just get the sensor tip up to temp quicker???

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Hi folks.

I've had an intermittent engine light for ages and had just assumed that it was one of the O2 sensors. It's been on constantly for a few weeks now but I got a code reader for Xmas so I tried it out yesterday and it displayed the P1135 code which we all know refers to the O2 sensor. My question is, is it definately the heater circuit that this refers to? Also, if it does-can I just splice into the loom of the other 'good' heater circuit to put the light out rather than spending 150 quid on a new sensor?

What does the heater do, does it just get the sensor tip up to temp quicker???

I wouldn't splice onto another sensor. They are there for a reason & monitor before and after the cat. If left as it is you will eventually suffer in loss of performance, consumption etc; believe me I know as the same sensor failed on me.

If you value you car :yahoo: your best option is to replace the sensor & you will be back up and running as normal.

Hope this doesn't sound too much doom n gloom but it's not worth cutting corners on thing like these.

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The check engine light comes on for emissions related issues so your can't won't pass the MoT with it on (or it shouldn't...!). With an O2 sensor down the engine management will be using a default fueling and as mentioned economy will suffer as most likely will performance. Best bet is to get the sensor changed and have a sweet running RAV once more!

You're correct in that the heater just heats the sensor up quicker from cold so it can control the exhaust emissions as soon as the engine is started from a cold start - needed for much more stringent emissions regs we have these days, rather than just letting the sensor be heated up by the exhaust gas.

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The check engine light comes on for emissions related issues so your can't won't pass the MoT with it on (or it shouldn't...!). With an O2 sensor down the engine management will be using a default fueling and as mentioned economy will suffer as most likely will performance. Best bet is to get the sensor changed and have a sweet running RAV once more!

You're correct in that the heater just heats the sensor up quicker from cold so it can control the exhaust emissions as soon as the engine is started from a cold start - needed for much more stringent emissions regs we have these days, rather than just letting the sensor be heated up by the exhaust gas.

Just re-read the above and to clarify the MoT fail with the check engine light on - the car will fail for the emissions related fault which put the check engine light on - not just because the check engine light itself is on.....

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Thanks for replies folks.

It sailed through an MOT in November when the light had been on continuously. If the heater is just to get the tip up to temp quicker then it should only really matter for the first two or three minutes of operation - I'm not convinced that this is a big enough problem to justify the £150 a new sensor is going to cost.

I'm not pooh-poohing your recommendations, it's just that I service the car myself and I know that everything else is in order. I'm not worried about things like bore-wash from extra fuel during warm-up as the default setting isn't going to be THAT excessively rich/retarded.

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  • 1 month later...

Just as an update folks, I spliced into the 'other' heater circuit this afternoon. At first the engine light would re-light after a minute or two, but after I cleared it for a third time it stayed off during a 10 minute idle and a 15 minute drive.

Since we bought the car, average fuel consumption over a tank has been around the 26-28mpg mark so I can an eye on this for reference. It's early days yet, but we'll see what happens...

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Apart from saving fuel the heater also increases the life-span of the CAT. So you may have to take that into account on the long term.:)

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Right, another update. My 'fix' lasted for two days until the engine light re-lit. I got around to sticking the reader on it yesterday and as well as the original P1135, it now shows a P0125 which points to the coolant sensor. I'm going to check the connections etc for corrosion and clear the fault codes. If it re0lights again then I'll remove the wires that I used to tap into the good heater circuit and see what happens.

Does anyone know what reading the coolant sensor should give at around 10C, or when engine is 'warm'??

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Hi ours has been like this now for the past 6 months and no one has any ideas its a common fault there is nothing wrong with your coolant its all to do or I think it is down to the lambda I changed the lambda and the heater fault went away but the other fault came on and the fuel dropped by 2mpg? The lambda is now back with denso for testing. I have pulled my hair out over this one and as for the MOT it passed that two months ago because the emissions were fine. So if you get any answers please please please let me know. If you do decide to change the Lambda dont get ripped of by Toyota go to euro car spares £84 and its Denso just that Toyota like to print their name on there as well and charge double.

Good Luck.

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Hi jako. Yeah, I'm happy that there is nothing wrong with the coolant sensor and I'm confident that once I remove the bridging wires between the two lambda's, that the coolant fault code will correct (or at least not re-appear after clearing it).

The way I see it, and this isn't necessarily the general consensus, is that the only snag is that the car will run richer for an extra couple of miles until the lambda tip heats up naturally. I could be wrong, and the management may stay closed loop all the time, but the mpg seems comparable over the entire course of my wife's ownership.

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I've a feeling the more you "Tap" in to the good heater circuit the more chance you have of overloading the heater circuit. :crybaby: This could cause any amount of damage to any sensors that are on that actual circuit-leading to more cost to yourself. :!Removed!:

My advice is to renew the damaged sensor-its there for a reason and will only make your car run better & more efficiently. :D

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I am also kinda intrigued what you mean by "spliced into" the other heater circuit. Each heater circuit is effectively seeing its heater as a resistance placing a voltage across it which causes a current to flow. (I=V/R)

I guess you have spliced the heating circuits so they are in parallel, which will mean the current supplied by each heating circuit is effectively cut in half. (So no chance of doing damage)

If the heating circuit just detects open or closed circuits this will fool the ECU, but I suspect that the heating circuit also detects current flow and if it is outside a set tolerance flags an error :-(

Ian

(PS If you have wired them in series then I suspect you will blow something very quickly, probably the other heater)

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I am also kinda intrigued what you mean by "spliced into" the other heater circuit. Each heater circuit is effectively seeing its heater as a resistance placing a voltage across it which causes a current to flow. (I=V/R)

I guess you have spliced the heating circuits so they are in parallel, which will mean the current supplied by each heating circuit is effectively cut in half. (So no chance of doing damage)

If the heating circuit just detects open or closed circuits this will fool the ECU, but I suspect that the heating circuit also detects current flow and if it is outside a set tolerance flags an error :-(

Ian

(PS If you have wired them in series then I suspect you will blow something very quickly, probably the other heater)

I may be mis-understanding what you mean, but that doesn't sound quite right to me.

This is going back nearly 20 years, when I worked on petrol EMS ECU design. Toyota's component supplier may have a different implementation to the explaination below, and/or things may have moved on, but looking at a toyota petrol EMS wiring diagram, it certainly looks like they use a low side drive (switch) for the lambda heater.

Below is a very simplified circuit for a lambda heater control. For a simple explaination, Q1 (A FET - Field Effect Transistor) can be considered as a switch. If you parallel up two lambda heaters (R4 and R5), they will both get roughly the same amount of current as before, BUT, to a first approximation, the FET now has to pass double the current it would normally. Fine, IF it is rated to do it!!! Double the current is 4 times the power dissipation (determines how hot the FET gets - the FET has a finite resistance and power dissipation is I^2*R). This may shorten the FET's life.

lambda.jpg

We also used to monitor the heater current. All the current flows through R1. R1 is a very low resistance. The current flow generates a small voltage across R1, which is amplified and passed to the microprocesssor. Putting two heaters in parallel, would probably make the ECU think the heaters are colder than actual and/or flag an error as you say. I'd expect the lamdba heater resistance to go up with temperature, but by putting two in parallel, you've lowered the total heater resistance.

We also used to turn off the FET, if we detected the FET drain (where the heater is connected to the ECU) getting shorted to Battery.

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Hi shcm I enjoy your posts, very interesting :-)

Not sure what "doesn't sound quite right to me"

My original guess was he was getting a P1135 fault (maybe wrongly) because on of the heaters in a Lambda sensor had burnt out and gone open circuit.

I was curious how he was getting round this error and I suspected (guessed) he was connecting two heating circuits in parallel across one working heater .

Ie two FET heater controllers effectively one R5.

Thus both heaters were seeing the same load, and it was reported that this seemed to temporarily (two days) remove his error code.

I suspected (taking out temp effects) this would halve the current through each of the two heater circuits and probably flag another error (if current was monitored), why this took two days is interesting. I guess its determined by the ECU error detection firmware ?

You seem to agree with this bit in the latter part of your post,

"Putting two heaters in parallel, would probably make the ECU think the heaters are colder than actual and/or flag an error as you say."

So I am not sure what doesn't sound right ?

A perplexed

Ian

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Hi shcm I enjoy your posts, very interesting :-)

kind of you to say! :)

So I am not sure what doesn't sound right ?

A perplexed

Ian

Ah, Gotcha!

It was the:

I guess you have spliced the heating circuits so they are in parallel, which will mean the current supplied by each heating circuit is effectively cut in half. (So no chance of doing damage)

that threw me. :thumbsup:

I read that as two heaters in parallel through one driver. The driving transistor in that case would sink approx double the current. One heater and two drivers, yes, agree, in theory, half the current through each driver. FETs in parallel will tend to share current. Bipolar transistors generally don't. I wonder what it uses :g:

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Moral of the story is................

........don't tangle with my boy. He has become like a Cyberdyne Systems T101 model Terminator and is now far more powerful than when I created him. However, he is a T102 MkIII and can even create plush interiors as well as complex electronics.

He'll be back :robot:

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