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Timing Belt Replacement Followed By Error Code P1135


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I just had my timing belt replaced at the recommendation of the Lexus dealer at a Lexus dealer for scheduled maintenance (91,000 miles). Within 3 days the Check Engine light and VSC light came on.

I took it to an autopart store who read a p1135 code "A/F Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)", to which I replaced today by myself with a brand new Toyota one (part number 89467 by Denso) A/F sensor. 30 seconds after clearning the codes (both through an ODBC2 computer and disconnecting the battery for several hours), the lights came back on and it re-read error code p1135.

Could the dealer and mis-timed my engine resulting resulting in a bad air fuel mixture that might cause this code? Any thoughts on if this is related?

Honestly after spending an $$$ arm $$$$ and $$$ a $$$ leg $$$ replacing the timing belt, all other belts, and the waterpump I'm honestly scared to go back to the dealer and face a several thousand dollar repair.

Thank you.

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Have you checked the vacuum hose behind the air cleaner? Sometimes this is left disconnected after repairs or servicing. Also, is your fuel cap sealing properly? I have read in this forum that each of these can cause the symptoms you mention. I will be following this post because I have the same thing going on. Good luck!

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Thanks for the reply and tips.

There are no disconnected hoses off of the aircleaner and I've super cleaned the Mass Airflow Sensor (MAS) with alcohol & Q-Tips with no luck, nor is it throwing a code related to that.

The fuel cap seems to be sealing properly, but how do you ever know? I might replace it just to make sure because that is a good thought.

The engine compartment is shockingly clean (I'd seriously eat dinner off of the top of it, or any parts within) which leads me to believe that there has never been any corrosion or abuse which I suppose could affect other wires.

Anyone...anyone? The coincidence of the timing belt change leads me to lean towards that, but as I mentioned I can't fathom another couple thousand dollars to deal with this issue.

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It's not the hose behind the airbox or the gas cap. If it was you would get an evap type code like P0440, P441 and P0446. Are you sure it was bank 1 sensor 1 that you changed?

Here is some info I had saved on that code on a RX:

"P01135 A/F Sensor Heater Circuit (Bank 1 Sensor 1) Replaced

You can ohm the 2 black wires and you will have an open circuit. The replacement sensor much read between .8 and 1.4 ohms to work properly and not generate the P1135 code. A Denso generic has a resistance of 8 ohms across the heating element and vehicle will still generate a P1135 code. The Bosch replacement would not correct the P1135 code. I did not measure the resistance across the heating element. Installed Toyota 89467-48011 which has resistance of 1.2 ohms and problem is solved."

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100% sure that I changed the correct sensor. Bank 1 Sensor 1 is located on the backside of the engine near the firewall, accessible from underneath the vehicle with a lot of twisting of the arm and contortion of the body. It was replaced with a brand new genuine Lexus/Toyota Denso sensor with the exact same part number imprinted on it which reads TOYOTA 89467-48011 DENSO 0200.

HINT: for people reading this post in the future, the most difficult part of changing this A/F sensor out is disconnecting the plug connection, which is actually accessible from the top of the engine with one hand, and from under the vehicle reaching up with another hand - yes it takes two people. There is a small slot on the female end of the plug near where the four wires go into the plug (the female side of the plug is not the end attached to the A/F sensor). Slide a very small flathead screwdriver into that slot which will release the male end of the plug while being pulled by your buddy reaching up from under the car. Because this plug connection is really hard to get to and takes two people, practice disconnecting the plug on the A/F sensor that comes off of the front side of the engine and is easily accessible. The plug connection for the front A/F sensor is grey and is on the drivers side between the air filter and the engine block. The front A/F is called Bank 2 Sensor 1.

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