P0135 might be bad ECM? 2003 2RZ-FE

I get code 135 when the truck has been on for 1-2 minutes. I can reset it and it comes back almost right away.

So is the A/F heater supposed to work right away when the truck is started cold?


How does the ECM decide to turn the heater on or off?


Does the heater still turn on with a cold start if the 0135 code has not been cleared?


Is there another malfunction or defective sensor input that would prevent the

ECM from turning on the A/F heater?


From the testing I did below, I think that either the heater driver circuit in the ECM is blown,or

there is a defective input to the ECM that prevents it from driving the heater.


I did recently adjusted the valves, clean the MAF, throttle body and IAC valve. The truck

idles and runs OK but the ECM will not go into closed loop operation.



I checked the resistance of the A/F sensor and it meets spec at around 1 Ohm.

Next I checked the EFI relay with a 1 Amp load and it is fine.

I checked for good continuity between the EFI relay and the red/white wire on the A/F sensor connector.

I checked for good continuity between the ECM and the A/F sensor on the white wire.

I checked that this wire is not shorted to ground or the battery voltage.

To confirm all of this, I put my current probe around one of the A/F sensor heater wires near the sensor and no current flows. My current probe has response from DC to 4 kHz and meter measures no DC or AC output from the current probe.

I also measured the voltage on the ECM pin for the A/F heater wire and it is a rock solid 14.1V with the engine running. Same deal with the red wire one pin over which powers the O2 sensor. this means that the ECM driver circuit is not pulling the pin low to allow current flow. If the driver circuit is simply an on/off switch or PWM, I would see a voltage lower than 14.1 V when the heater is on.

EJPHI

 

Physical damage to the harness ??

Have you looked for this ??

 

I Ohmed out all of the wires from the EFI relay and ECM to the A/F ratio sensor. I also measured the current through the circuit, and verified that +14 was present. So I think I am OK there.

The wiring harness is a tight fit around the valve cover and I had to push it around some to gain access to the rear valve cover bolts. I don't think I did anything too rough, it possible though that I created an intermittent short that blew out the heater driver.

The service manual trouble shooting chart for P0135 says that the either the ECM is bad or the connector pins are not making good contact.

 

i work at the dealer and never seen a ecm cause that code
the heater is part of the sensor so if its bad or doesnt warm up in a certain amount of time the ecm
will throw that code. i would replace the sensor with a oem one and see what happens

 

Hey Blacktaco,

Thanks for the reply. Since you know about this stuff can you tell me if any malfunctioning sensor input would prevent the ECM from driving the A/F sensor heater circuit?

 

the heater inside the sensor is the issue. unless you have bad wiring i would replace the sensor and clear the code and see what happens.
the ecm turns on the heater and it has a certain amount of time to get up to temp and if it does it will throw a code

 

Thanks Blacktaco,

So there are no other ECM input that are checked before turning on the A/F sensor heater?

BTW I measures the resistance of my A/F sensor heater and it is in spec at about 1 Ohm. I also connected my spare A/F sensor and still had no current draw or any sensor heating.

BRRR Wisconsin!! I grew up there

 

Spent some more time on this problem. The sensor heater worked well for a few minutes, I could see a reasonable voltage drop between the white heater wire on the ECM connector and ground. With my meter I could see an average voltage of about 5V and an AC voltage of 4V which is consistent with working PWM. My Scan Gauge indicated that the engine was operating in closed loop.

After a few minutes it went back to open loop and showed P0135 again. I tried to find an intake or valve cover leak with my propane tank and a hose, but had no luck. Through all of this, I hooked my meter up across the white heater wire at the ECM connector C pin 4 and the B+ input on A pin 16 which is the same node as the EFI relay output that sources the +14V to the A/F sensor heater. After the fault returned, the voltage read near zero which means no current was flowing, and when I shut off the engine I read 1.6 Ohms which means the the heater and wiring are AOK.

Could it be that the sensor side of the A/F sensor is bad and is causing the heater circuit in the ECM to shut off when it does not respond correctly.

Next step is to hook up my more advanced EASE scan tool and/or just replace the sensor even though it is stupid to throw parts at a problem without knowing the root cause.

I still have to ask what other inputs does the ECM use to decide that driving the A/F sensor heater circuit is AOK?

Does anyone here know?

 

I would agree. While I've only dealt with a handful of these, it's always been a bad A/F sensor.

 

Sure it is almost always the A/F sensor. But not this time

Lets continue the conversation in the thread I started after I solved the problem.