ODBII PO135 code


Old 06-24-06, 01:52 PM
Thread Starter
Join Date: Jun 2006
Posts: 2
ODBII PO135 code

Hi all,
I'm hoping someone here can help me. I have a 2002 Isuzu Rodeo 3.2L V-6 that has a Check Engine light on. I stopped at Advanced Auto Parts and they did an ODBII scan for me and it reported the following errors:

DTC (Codes)

PO135 O2 Sensor Heater
Circuit Malfunction
(Bank 1 Sensor 1)

O2 Sensor Heater
Circuit Malfunction
(Bank 2 Sensor 1)

O2 Sensor
CKT No Activity
Bank 2 Sensor 1)

DTC Pending (Codes)

PO135 O2 Sensor Heater
Circuit Malfunction
(Bank 1 Sensor 1)

PO155 O2 Sensor Heater
Circuit Malfunction
(Bank 2 Sensor 1)

The guy at Advanced told me there were 4 O2 sensors on my vehicle, 2 before the Catalytic Converter,and 2 after. He said the Sensor 1 was before the Cat, and he wasn't sure what Bank 1 and Bank 2 referred to. I would assume (I really hate to do that) that it refers to the bank of cylinders on the engine, but I'm not sure if Bank 1 is the driver's side or the passenger's side. Since the codes seem to indicate that Sensor 1 on both banks is bad, that doesn't really matter that much, I'll just buy 2sensors and replace both that are before the Cat.
I have 5 questions:
1. Is really is Sensor 1 before or after the Cat?
2. Which side of the vehicle is Bank 1?
3. Should I just replace all 4 sensors at one time?
4. Is there a special socket for O2 sensors?
5. Do the sensors come packaged with anti-seize compound, if not, is it required?

Thanks in advance
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Old 06-24-06, 03:58 PM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
An O2 circuit malfunction does not nessecarily mean the O2s are bad

If replacement were needed on a few, I'd replace them all
A special socket is available
Anti-seize compound may or may nor come with the sensors
It depends on the company/retailer

How many miles are on this vehicle?
Old 06-24-06, 05:16 PM
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Join Date: Feb 2005
Posts: 435
Before you do anything about the O2 sensors, let me ask you this first. How's the engine running at idle?, does the idle rough? or does the idle is higher than normal?.

I've seen too many Rodeos came in for those O2 sensor codes but only 1 out of 10(or more) really needs O2 replacement, most if not all of them are have the same common problem of intake manifold gaskets leaks, if yours is less than 70K miles, bring it back to dealer for warranty repair, oh, BTW, have you check and see how much of each O2 sensor cost?.
Old 06-24-06, 08:13 PM
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Join Date: May 2003
Location: USA
Posts: 1,459
Sensor 1 is before the catalytic converter. Sensor 2 is after. The Bank 1 & 2 refers to the left side and right side of the V-type engine separately. The Bank with the number 1 cylinder is always Bank 1, Bank 2 will start with cylinder #2 on your engine. Not sure, but I think Bank 1 on your vehicle is on the left side (drivers side) The easiest way to tell is to look at the engine from the fender side. Which bank is farthest foward? That is your Bank 1.
If you only had one sensor failure then I would say it is likely a sensor issue, but you have the same problem with 2 different sensors, Plus the inactivity code. I dont see how an intake gasket will cause these codes as the heater should not be effected by this. Unless there were coolant getting in the exhaust somehow and shorting out the sensors. Then I would think of many other problems (codes) you should be seeing for that. The inactivity code (P0154) just means that the sensor is not registering the expected rich or lean switching condition. It usually means that the sensor is stuck in the middle of the voltage range and is not "moving". If this is the case, then the sensor will definately need replacing, but not before you find out why you have so many O2 codes. I wouldnt just replace the sensors until you know whats causing them to be bad.
There are special sockets for O2 sensors, but if there is plenty of space a 7/8 or 22mm wrench will work just fine.
Most OE and aftermarket sensors come with Anti-sieze already on the threads. I have seen some that had a small package in the box with them.
I would recommend getting it checked out before throwing parts at it.
Hope this helps ya,
Good Luck,
Old 06-25-06, 04:43 AM
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Join Date: Feb 2005
Posts: 435
Intake manifold gaskets leaks will creates lean burns condition, un-metering vacuum entered the combustion chambers after the MAF, when ECU received signal from O2 sensors saying "O2 high/voltage too low", ECU looks at the MAF and variuos related sensor including "load" and "speed" to adjust air/fuel, all the signals came to ECU are within spec but O2 sensors keeps saying it's too high of O2, ECU does not agree with that input therefore, tunrs on MIL with all kind of O2 sensor codes.
Old 06-25-06, 07:35 PM
Join Date: Dec 2001
Posts: 2,538
what billys68ss was saying is that a vacum leak will not cause a heater circuit code for the o2 sensor, sure it can cause a lean exhuast code but that isnt one of the codes stored, remember that there is several codes that can be set for each o2 sensor.
you can usually test the heater element in the o2 sensor with an ohmeter, if the lights been on for a long time it isnt that uncommon for it to need 2 out of the 4 o2 sensors but wouldnt expect the heater circuit to just go bad on 2 sensors at the same time.
Old 06-26-06, 06:39 AM
Thread Starter
Join Date: Jun 2006
Posts: 2
ODBII PO135 code

Thanks to all who have replied. I have about 63K miles on the vehicle. I wasn't sure if this was covered under the 7/70 warranty or not. I guess a little research on that could very well save me some money and headaches.

Again, thanks to all.

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