2000 Avalon with P1135 and P1155

[sdpramanik]

I had some repair work done on the intake manifold of my 2000 Avalon with 125K miles. There was some oil leak from there. Now 1 week later the CEL comes on with codes P1135 and P1155. Figured that was Bank 2 Sensor 1 (front of engine exhaust manifold ) and Bank 1 Sensor 1 (rear engine exhaust manifold ) A/F sensor heaters going bad. Both heater circuit resistance was too high. Had them replaced by the local mechanic with OEM equiv. Denso 234-9021. Denso makes the actual Toyota sensors (with the Toyota labels).

After an hour the CEL is back with same P1135 and P1155. Mechanic says resistance is within range on both sensors. However he checked the wiring and the A/F Sensor Heater Relay and he is seeing +1 V higher. All fuses are OK.Wondering what to do now. Should I replace the Denso ones with the Toyota branded ones? Could the ECU be bad?

[avalonshoe]

toyota branded ones are actually densos

[TedL]

I've replaced AFR and O2 sensors at 100k just as preventive maintenance, so don't feel like you've wasted the $. They get less accurate before going bad. As noted above, Denso makes the OE part. If you looked at the ones removed, you'd have seen the Denso brand on them, along with the Toyota P/N.

Someone needs to be looking at the data stream (freeze frame data) to see what parameter is out of range. That will allow for more focused troubleshooting. In general, when work is done and problems arise close on, look for bad/damaged/loose wiring, connections, etc.

The diagnostic flow charts almost all allow for the possibility of a bad ECU (for completeness), which is really pretty rare. You need to find a shop that takes pride in its diagnostic ability, invests in the tools and training, and does the work needed.

[avalonshoe]

I just replaced bank 2 sensor 1 this morning. You can buy it for under $25 shipped providing you do some wire cutting. My CEL is gone and code for thermostate gone. That O2 went about 180K miles and still did not affect my gas mileage when it was going bad. I could have easily went a few more weeks/months on it.

[careh]

I had a similar problem. It started with a check engine light on my 2000 Avalon with P1135 and P1155 codes. The engine (a replacement) has 60,000 miles on it - however the car has 180,000 miles on it. One of the air/fuel sensors was replaced last year when the replacement engine was put in.

The garage checked both fuel/air sensors when the codes appeared - and both had failed /open heater circuits. Both sensors were replaced with Denso 234-9021 air/fuel sensors and all was well for a couple of weeks. Then the check engine light came back on. The P1135 and P1155 codes had returned. Over then next few weeks various tests were done. First thing - the grounds were checked and just to be sure - cleaned. Next the car was brought in overnight so they could scope the engine when cold. Everything checked out normal. The relay was ok - the wiring was ok - power was getting to the sensors. My garage asked on his mechanic forums but the answers coming back were for the most part all ones he had tried.

I began googling for similar problems and saw people talking about things such as cleaning the mass airflow sensor MAF reduced fuel pressure caused by a bent fuel line, clogged fuel filter, or faulty fuel injector. Tips to look for leaks in the vacuum hoses, leaks in the exhaust manifold, that Denso sensors were 'less sensitive' than 'Toyota Red Box sensors'. The computer (ECU) was a last point of failure - however it sounded like it rarely failed.

A suggestion was to replace the air filter - which I did. The old one was not especially dirty - but now there was a new one in there. I cleared the codes and after a couple of short drives the check engine light came back on - now with a new code - a P1130 plus a P1135.

Another suggestion was to disconnect both positive and negative leads from the battery and leave it for 1 hour. I am guessing this did the dual purpose of clearing the codes from the computer and resetting the computer. So I did that as well. After doing that I got a P1155 and P1135 code again.

At that point I put in an Autel Maxirecorder - data logger - which was showing P1155 pending and P1135 stored codes. A few days later it had P1133 pending and P1135 stored. A few days later only the P1135 stored was there.

My garage was getting ready to test the installed sensors and then for good measure replace them when all of a sudden one day the check engine light went out. I used a scan tool to see that there was only a P1135 code pending. I cleared it and since then (5 days, multiple engine runs of both high and low speed) the check engine light is out, no codes are showing on my scan tool and the maxirecorder is showing everything running just fine.

So it looks like - in some cases - patience is a virtue. I hope this helps someone else with a similar problem.