daltongd

I have a 2001 RX300 with 225K miles. Recently did a spark plug tune up and made a home made injector cleaner and bench tested and cleaned all the injectors. Shortly after that the rear A/F sensor went out and shortly after that the Fwd A/F sensor went out. Each time I did a resistance check and each time the sensors had a open circuit. I installed Toyota A/F sensors both times.

The P1155 code came back about 3 weeks and a couple of thousand miles later. I have done a resistance check of the A/F sensor and it ohms out just fine. I cleared the code and it came back 200 miles later.

Anybody know where to go from here? Everything you read says to replace the senor on a P1155 but what do you do if you have that code with a good sensor? Is that even possible?

carguy07

Any chance there is something else tripping it, like an exhaust leak?

code58

You are in fact checking the resistance on the FRONT sensor (the 1 by the radiator) aren't you? I believe the 2 black wires are the heater wires (which is what P1155 is indicating). It would be HIGHLY unusual if a Denso sensor with a couple of thousand miles went out. Anything is possible but if the front sensor ohms out OK (even a continuity check should confirm it), you obviously have a problem elsewhere. People often get Bank 1 and Bank 2 confused.

Baetke

P1155 is an A/F sensor heater circuit malfunction for Bank 2. Since you already changed the A/F sensors I would check the A/F relay and A/F fuse as well. These two components are common to both the Bank1 and Bank2 sensors so I would have expected you to see a P1135 DTC as well if one of them were bad. Could also be a wiring harness or ECU problem. Basically, try to verify that you are getting voltage to the A/F heater leads.

daltongd

There is not a exhaust leak as far as I can tell. I don't hear one anyway. I can try to investigate that further.

Yes I am checking the A/F sensor that is closed to the radiator.

I will keep working it and let you know what I find.

Is there any way it could have something to do with the fuel pressure? Could the fuel pump be having an occasional issue?

gazi001

Check the wiring harness and voltage of A/F sensor.

code58

Since DTC P1155 points directly to the heater in B2S1 and the only purpose of the heater is to bring the sensor to "closed loop" quickly (like getting your automatic choke off quickly to eliminate excess polution) as well as keeping the temp up for "closed loop" as when going down a steep grade with no throttle applied. The rest of the time it's just along for a free ride so I don't think it would have anything to do with the fuel pressure. Maybe the A/F ratio sensor part of the sensor would, but not the heater. If it had excess pressure and caused it to run cooler because of the excess fuel maybe, but the heater and the ratio sensor are 2 seperate entities inside the A/F ratio sensor housing. Curious soul that I am I cut one apart that had a failed heater to have a look see. Indeed the heater element had a break in it. The sensor part will work just fine even with the heater broken, just won't respond as quick as the "rapid reponse" when the heater is working.