99 Camry 4 Cyl 5SFE California

Wife's car threw code 1135 A/F Sensor Heater - Short Circuit Or Open

93K miles. Oxygen sensor heater resistance checks out ok (.8-1.4 ohms).

Replaced sensor anyway that the code was getting thrown intermittently ($220 sweet, lol) and still have same code thrown a few days later.

The next step is to replace the ECU / ECM as the fault is likely inside the ECU. I wish the code was more specific as to whether the failure was from open or short circuit. Short isn't likely as there is 1 ohm across the new sensor but it's so hard to tell with such a small resistance.

The circuit runs from battery positive to the ignition relay. From there the heater is powered with batt power and then the circuit continues back to the ECU. This is where the heater could be turned on or off by the ECU.

The 12 V exists back at the ECM harness where it's supposed to be with the ignition on indicating the circuit is at least not open anywhere along the line.

It seems to me like a failure of the ECM. I'm a little disappointed that this happened with less than 100K miles and only 9 years life.

Anyone know the price on one of these? I assume somewhere around $400 at the dealer?

Anyone have one of these fail this way before?

Second options on my diagnostics?

Post edited by: hobbist, at: 2008/10/08 16:25

You have no idea what you are talking about.

Post edited by: hobbist, at: 2008/10/08 16:26

The code is for the heater circuit on the A / F sensor. It has nothing to do with the engine exhaust.

Look up the Bosch Wide Band O2 sensor on the net to understand. (http://www.wmsracing.com/o2/tech.htm)

95% chance the CPU is bad and that's what we have ordered. $729 for the unit with $100 core.

Post edited by: jmborchers, at: 2008/10/08 01:22

sorry i misunderstood i though you where talking about oxygen sensor it also has a heater .i was wrong and with draw statements i did not see a/f sensor you are right sorry. i have erased my statement i was wrong.

Post edited by: hobbist, at: 2008/10/08 16:32

No problem.

The ECU pulses the circuit to heat up the heater. The heater drive circuit goes through a resistor in the ECU and then through a transistor or solid state relay. Either the solid state relay has gone bad and it can no longer drive current through or the detection circuit to detect the current flowing doesn't work anymore. It's one or the other according to the code thrown.

My guess is that the drive circuit is kuput and the heater can no longer fire.

When the heater can no longer fire, the ECU has to put the engine control into safe mode. In this mode it doesn't monitor the A/ F mixture or tune the engine because it can't read the sensor. Therefore the engine becomes less efficient.

There is no guarentee it is the ECU but the dealer's service guides I have point to that as the direction. The only reason I replaced the sensor first even though the dealer guide said it was probably the ECU is because the sensor is cheaper and the sensor is already near the end of its life.

The good thing for us is this is the car's first non standard maintence repair.

$1K in 3 years is not so bad.

The computer is now replaced.

No fault light on startup. Turn key off and on a few times. Still no light.

Then I purposely disconnect O2 sensor. Upon next car start computer code comes up 1135 but has no MIL because this particular code needs two successive faults in order for MIL and freeze frame to be stored.

So, it appears this computer can detect correctly whether theres an open circuit or not, that's a start. I don't know what the old computer did on this behavior.

With engine warmed up O2 sensor is reading correctly at idle and racing engine. What will happen when car isn't warm remains to be seen. The oxygen sensor is supposed to be used only when the exhaust gas is cold.

On the old computer the first fault was caught displayed that the coolant was 77 degrees when the fault occured and MIL came on.

According to the dealer's manual. The computer is the cause based on the diagnostics they recommend.

Time will tell...

Still the dumb light came on a few days later. This is a pain in the neck problem.

Everything checks out according to the dealer's own manual.

My guess is another sensor has something wrong with and there's a bug in the MPU itself on the car and it's throwing the wrong code.

Dealer's book points to MPU so even though they don't accept electronic special order returns I'm going to push for it either from the dealer or Toyota if I have too.

The problem itself is intermittent. Sometimes when you start the car up the heater circuit for A/F sensor works and sometimes not. The problem is caused by the computer itself not engaging the circuit because the power is always available at the computer which is the end of the circuit.

I bet many other Toy customers may also have this problem.

Only one code is thrown. All other sensors appear to be operating correctly.

Post edited by: jmborchers, at: 2008/10/12 03:07

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did you solve your 1135 problem?

i have similar 99 Camry Calif emission with same problem.
along with 1135 code
i also have 0125 code Coolant Temp Below normal at closed loop.

check engine light coming out after reset very quickly (driving few miles at warm engine temp)
noticed that none of the monitors get set

looks like thermostat works fine
already installed new A/F sensor from Toyota no help.

Thinking of ECU as next step,
possibly check rear O2 sensor make sure it doesnt cause 0125 fault...

let me know if any success in resolving this issue

thanks