OBDII PO135 code


Old 09-04-11, 07:09 PM
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Join Date: Sep 2011
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OBDII PO135 code

I had my friend plug his reader into my car because it has been over heating and I just replaced the thermostat and that didnt help at all . . . I drive a 2003 Buick Rendezvous 3.6L AWD and when he did it gave him these two codes and I dont know anything really about cars . . .

HO2S-11 (Bank 1 Sensor 1) Heater Circuit Malfunction

HO2S-12 (Bank 1 Sensor 2) Heater Circuit Malfunction

but it is also burning through coolant extremely fast too, can any point me in the right direction? Because I have read that all because it gives you those codes doesnt mean they are bad . . . please help if you can thanks!
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Old 09-05-11, 05:48 AM
Join Date: Mar 2009
Location: Texas
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Engines are not suppose to 'burn through coolant'. Possible causes:

Leaking head gasket
Leaking intake manifold gasket
warped or cracked head

Is there any sign of white smoke and or water coming out of the exhaust?
Any signs of coolant in the engine oil?

The GM 3.6 engine is known for issues around cylinder head but especially around leaking intake gaskets.
Old 09-05-11, 06:14 AM
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Just to add since equinox didn't touch on it; those codes are for the oxygen sensors. The coolant being burned is affecting the oxygen sensors in the exhaust system.

Bank "1" should be, I think, the left side, so that's likely where your head or intake gasket is shot.
Old 09-06-11, 04:29 PM
Join Date: Sep 2011
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heater circuits in o2 sensors are for getting the system into closed loop (fuel control) sooner they have nothing to due with the sensors ability to register hc levels in the exhaust this is a 4 wire sensor and you will have to check the sensor heater for resistance before you condem it

i would do a visual check for coolant loss first and then do a combustion gas test in the cooling system if no leaks are visable this will tell you if you have a head gasket leak into cooling you can also remove the upstream o2 sensor and examine it for antiofreeze contamination one of these will bear fruit for you
Old 09-07-11, 08:30 AM
Join Date: Aug 2011
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Similar to the gas test stated by JPICKLES, if you are able to, put your coolant system under a pressure test by applying air pressure through the radiator. It takes a required tool, perhaps asked Auto Zone or other auto part shops if they could lend you the part.

What this test should do is give you an idea of if your head gasket has a leak in it. When pressure is applied and there are no leaks, the pressure level should be a a decent level. If there is a leak in the system, namely the head gasket, the pressure will be higher since the air pressure is pushing the coolant into the cylinders.

Also, a nice little test I've been told to use that can also help to see if you have a bad head gasket, by taking off the radiator cap when the engine is cold, and start the engine. Wait awhile for the engine to warm up, and if you begin to see a lot of bubbles or foam develop in the coolant, that COULD mean there is a leak because the air in the combustion chamber is being forced into the coolant system through the leak, resulting in overheating and possible coolant lost.

How is your car overheating? Does is overheat sitting in one place, at low speeds, high speeds, long distance, etc.? I had a overheating problem where it would get too hot on long distance highway driving and there was a small loss of coolant, but the problem was a bad water pump. If you could tell us a detailed explanation of how your car overheats under what conditions, we could possibly help you further.

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