Odd P1155 Issue

First off, it was back in 2012 when Paul, Dylan, and others whose names have gone the way of some Black Sabbath lyrics, helped me quickly diagnose and solve a problem that four mechanics and over $2,000 in parts and labor couldn't figure out, IN JUST A COUPLE OF POSTS: bad downstream O2 sensor in my '97 Civic. You guys are awesome.

I'm back, frustrated again, with a 2001 Toyota Rav 4, 2.0 VVT-i, 45,000 miles.

The CEL comes on when I sit parked and idling for a while (15 minutes or more). DTC is P1155, A/F Sensor Heater Circuit (Bank 2 Sensor 1). However, if I drive on the highway for a while (30 minutes or more), it goes out. Repeat constantly. There are no engine performance issues I can notice.

I checked the A/F sensor's heater wire resistence, which was 2.6 Ohms, which I believe is within spec, and then the fuses, EFI main relay, and ECM voltage output, and all are fine.

I have a new sensor standing by, but I always remember the motto of this web site: "Don't Be a Parts Changer", and I just want to be sure of what the problem is.

I've also included the freeze frame data from when the DTC triggered. I just don't know how to interpret it, aside from the STFT shouldn't be stuck at 0% should it?

Freeze Frame Data:
• PID : Description : Value
• 03 : Fuel System Status : System A: Closed loop - using all oxygen sensor(s) as
feedback for fuel control System B: Closed loop - using all oxygen sensor(s) as
feedback for fuel control
• 04 : Calculated Engine Load Value : 14.9 %
• 05 : Engine Coolant Temperature : 88 °C, 190 °F
• 06 : Short Term Fuel Trim Bank 1 : -2.3 %
• 07 : Long Term Fuel Trim Bank 1 : -2.3 %
• 08 : Short Term Fuel Trim Bank 2 : 0.0 %
• 09 : Long Term Fuel Trim Bank 2 : 0.0 %
• 0C : Engine RPM : 711 rpm
• 0D : Vehicle Speed : 0 km/h, 0 MPH
• 0F : Intake Air Temperature : 68 °C, 154 °F

Any ideas?

I think I would start buy doing an unplug test on the wiring using a tungsten bulb test lamp as a dummy load, and watch if the lamp lights fully.
Using a test light puts a enough load on the circuit to give a realistic test.
Reconnecting the senors check the voltage between both the heater connections and ground.

I would also test the resistance of Bank 2 Sensor 2 to give a comparision.


The reason you are only seeing a P1155 fault code and no others is likely the computer will test the heater circuits on initial start up and then ceases further test on the B1S1. The reason for the zero fuel trims on bank 1 is the engine computer is ignoring the output of B1S!

bashea wrote: First off, it was back in 2012 when Paul, Dylan, and others whose names have gone the way of some Black Sabbath lyrics, helped me quickly diagnose and solve a problem that four mechanics and over $2,000 in parts and labor couldn't figure out, IN JUST A COUPLE OF POSTS: bad downstream O2 sensor in my '97 Civic. You guys are awesome.

Hey, I remember this one! Welcome back! Did you ever get around to replacing the control arm bushings?

I like Andy's suggestion of using an incandescent test light on the heater wires at the sensor, just to make sure of it's load carrying ability. If it shines bright on the power side and control, then I wouldn't hesitate to change the sensor.