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Peter Bagley
Peter Bagley, Auto Service Technician
Category: Toyota
Satisfied Customers: 684
Experience:  master tech at Toyota dealer
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I believe that my ECU may be faulty. I have p1135 and p1155

Customer Question

i believe that my ECU may be faulty. I have p1135 and p1155 codes, and have checked the resistance of the heater circuits in both sensors (bank1 and 2 sensor 1). I have also checked the voltage/amperage of the circuit at the ECU and found it to be 12v and within the .25-8A range.
JA: Which particular sensor are you asking about? And have any trouble codes been triggered?
Customer: are you a real person?
JA: I'm an assistant to the Toyota Mechanic. I work with them to help customers like you.
Customer: sorry, have to check!
JA: What is the model/year of your Toyota?
Customer: 2001 RAV4, 2.0L 4WD
JA: Are you fixing your RAV4 yourself? What have you tried so far?
Customer: did you read my previous statement?
JA: Anything else you want the mechanic to know before I connect you?
Customer: did you read what I typed above?
Submitted: 9 months ago.
Category: Toyota
Expert:  Juan Crespo replied 9 months ago.

Hi there. Sorry about our automated "Mechanic's Assistant" - it's just software. I, on the other hand, am a real tech (albeit retired) and I'll be reviewing your issue. Please allow me a few minutes to do so. Be back in a bit...

Customer: replied 9 months ago.
No problem, thanks.
Customer: replied 9 months ago.
Resistance on the sensors were in the 1.8-2.3 range with the engine warm but not running.
Expert:  Juan Crespo replied 9 months ago.

Looks like you've done your homework on this one. Basically, this issue can be caused by one of three things; bad sensor heater, bad circuit (fuse, relay, connection/wiring) or bad ECU - you mention sensor heater resistance at 1.8-2.3 range. Have you checked the A/F fuse and measured heater circuit amperage draw? - that would actually tell us if the ECU is energizing the relay.

Expert:  Juan Crespo replied 9 months ago.

Just in case you needed, I'm attaching a couple of graphics; one shows the location of the A/F fuse and relay; the other shows the circuit diagram.

Please let me know if you need more detailed instructions.

Best Regards.

Customer: replied 9 months ago.
current at the Ecu is .17amps for HAF1 and .07 for HAF2. Both are well below the operating range, correct? What does his tell us?
Customer: replied 9 months ago.
I took the relay out and tested it with a separate 12v power supply and the continuity setting on my multimeter, and it was engaging and passing current.
Expert:  Juan Crespo replied 9 months ago.

What we need to find out is whether or not the circuit is getting current and if so, how much. In other words, we need to find out how many amps are being drawn by both heaters - we can't find that out by measuring at the ECU.

Does the A/F fuse have 12 volts going through it? Is the A/F relay being energized by the ECU? Can you feel it "click"? Also, I might be able to help better if I knew the brand/model of the meter you're using...

Customer: replied 9 months ago.
Ah, I see what you mean. There is .13amps at the 12v fuse, and I can't tell if the relay is engaging, because I am troubleshooting alone right now. I'll update you in a little while when my wife is home to turn the key for me.
Expert:  Juan Crespo replied 9 months ago.

Not a problem. How about that meter brand and model?

Customer: replied 9 months ago.
Meter is a Southwire 10040N.
Expert:  Juan Crespo replied 9 months ago.

I looked up that meter and, according to the website, it is kind of a household-type meter, not something that could be used for our purposes as it does not have an ammeter function - which explains those readings you were getting. Can you get a hold of an automotive multimeter equipped with ammeter function?

Expert:  Juan Crespo replied 9 months ago.

Click here to see an inexpensive model from Harbor Freight - only draw back is that it can only handle currents of less than 10 Amps.

Customer: replied 9 months ago.
Funny, I actually have that one too. I put it on the test point of the A/F fuse and it appeared to go into overload and then started really heating up the probe leads.
Expert:  Juan Crespo replied 9 months ago.

Please don't take this the wrong way, but it sounds like you're not familiar with automotive electrical circuits or the tools used to test them. If that's the case, everything is OK, as I am a retired tech instructor and would not mind taking you through the procedures.

Let's start with measuring voltage at the A/F fuse:

  1. turn ignition switch ON
  2. set your meter to the 20 volt mark on the DC volts range
  3. place the meter Black probe on the battery negative post and the Red probe on either one of the two little points showing through the top of the A/F fuse
  4. what voltage is the meter showing?
Customer: replied 9 months ago.
Hah! I'm pretty experienced with electronics and such, just not that familiar with automotive. We are just trying to measure D.C. amperage, right?My meter reads 12.2 when I do that
Expert:  Juan Crespo replied 9 months ago.

Actually, we were trying to measure DC voltage at the A/F fuse. I'm sorry, but it is just taking too long between your reply and my responses... I'll opt out and re-open your question so other experts can chime in. Please do not rate or reply until another expert responds or the site will cycle the question back to me.

Customer: replied 9 months ago.
I waited for another tech, but I received no reply. I'd like to continue with you, as I think we were close to figuring out the problem. I'll be working on the car again tomorrow, and I will chime in here when I'm getting started. I think you may have gotten an improper pictures of my experience level with electricity, and I will gladly demonstrate that tomorrow. Perhaps we could chat on the phone and take care of it quickly. Thanks!
Customer: replied 9 months ago.
I am now home and would appreciate a little more advice. I believe we're close to figuring this out!
Expert:  Peter Bagley replied 9 months ago.

Hello and thanx for using Just Answer . I see you need further assistance ? I'll see if I can add some further help.

Expert:  Peter Bagley replied 9 months ago.

Click the link for the efi wiring diagram. Check the voltage at HAF1 and HAF2 W/L and W/R wires on page 2 of the pdf at the engine computer. The voltage needs to be 12 volts with the key on and the engine not running and everything plugged in and the AFR fuse good. Start the engine, within a couple of minutes the voltage should drop to 0 volts. The computer monitors this voltage drop to determine if the heater is working. If the voltage does not drop with in a few minutes you will probably find that the drivers in the computer are no good. In some rare cases the AFR sensor can short out and normally blows the fuse but it can damage the driver in the computer.

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