P1135 Help

Hi all,
Just joined the forum and it is really a good site. I am trying to help my neighbor with his 2001 Prerunner with 3.4 l.His check engine light is on. The local garage looked at it and told him to not worry about it, that it was the O2 heater circuit and not a big deal. I have a scanner and do most of my own work so my neighbor asked me to take a look. First check had P0300-random misfire,P0303-Cyl #3, P0306 Cyl #6 misfire and P1135 Air/Fuel heater circuit response fail. Cleared the codes and restarted the engine. Code P1135 came back on immediately. Drove around for a little while and monitored live data. Fuel code fails and stays in Open Loop mode. Fuel short term trim level stays at zero. If code P1135 is heater circuit, I thought that was for initial start up and once engine reached operating temps was no longer a factor. Engine never went to closed loop and misfire codes did not return. I dont think the O2 sensor will even start to work until engine fuel goes to closed loop. I like to diagnose the problem before buying parts. Any expert code readers on the forum that could give me some clues on what to look for? I don't remember what the MAF data was but thought it was high (maybe 8 gps at idle and 22gps driving about 25mph) is that about right? I will be looking at it this weekend and just trying to gather some data. Thanks for any help.

Ed

 

sounds like a bad maf to me. it uses a heater and determines airflow by how much electricity it takes to keep the element at a constant temperature.

 

doht. 5 second google search failed me. and that's really weird that you're getting O2 codes with misfires. that doesn't make any sense. you might have more than one problem.

an intake problem would make a lot more sense though if you're getting misfires.

 

Sham,
I am thinking maybe more than one problem also. Since the misfire codes have not come back yet, I am going to focus on the P1135 first. The engine fuel system not going into closed loop operation bothers me first. My son's car takes about 15 seconds to go to closed loop on start up, this Tacoma never does. I have to learn how the system operates. I am going to check resistance at the two black wires of the O2 sensors and clean the MAF sensor for starters. Any other suggestions would be appreciated. If it was my truck I would change the sensor right away but don't want to do that and have it be something else on my neighbors car since those sensors are so pricey. Thanks

Ed

 

98Tacoma27, Good info thanks. I have a technical background. I am trying to get my hands on an o'scope to see if I can really test it out. I just like to see how things work.

Ed

 

i'd check the heater before you even bother with the o scope. usually on heated sensors the heater will go out before the actual sensor does. so the o scope readings would be irrelevant if the heater is burnt out anyway.

basically, when your 02 sensor goes out, your car won't run any different, a light on your dash will go off, and you'll probably get worse gas mileage. they don't affect drivibility. which is why the sensor and misfires are probably 2 separate problems.

02 sensors play a much smaller role in overall fuel trim than most people think.

 

Sham,

I will probably do that. One question I have is once the truck has been running awhile and up to operating temps does the heater even matter then? Shouldn't it start working once it gets hot anyway?

 

maybe. but if the heater has an open the ecu might just decide not to use any info from the sensor at all.

 

TThanks for all the help. I will report back what I find.

Ed