Have Toyota Questions? Ask a Mechanic for Answers ASAP
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...
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.
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.
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...
Not a problem. How about that meter brand and model?
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?
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.
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:
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.
Hello and thanx for using Just Answer . I see you need further assistance ? I'll see if I can add some further help.
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.