I think I may have fried or destroyed my exhaust temp sensor somehow soon after fitting my decat yesterday. I'd seen it flicker on before driving to the garage when letting off on low rpms (2-2,500 or so). After fitting the decat and hooking up the sensor again I drove around. After about 20 minutes I saw the exhaust temp sensor start to flicker on and off again and then just came on and stayed on. I pulled over and let the engine cool down and started it up again. Sensor is staying on from the start now, even with a stone cold engine.

Now I don't know if the car is running lean or timing is off and the temperature really was high, although I don't think either are happening. But my exhaust warning light is constantly on now which is a bit of a distraction. Am going to be getting an EGT gauge anyway so is there any way to stop the exhaust/temp warning light from coming on?

Cheers for any advice you can offer me

 

The Heat Hazard switch is located under the passengers seat. Unplug it.

 

Like the mailman, HAILERS always delivers. Thanks man

 

Hmmm... maybe not as simple as all that. I reached under my passenger seat (strangely, the exhaust temp sensor goes through the passenger floor on both the LHD US models and the RHD Japanese models) and disconnected the heat hazard sensor. Started the car up and still getting the heat warning light.

Checked the FSM and it said that the ECU would get the following voltages back from the sensor:
Idle (floor temp below 110C) - Approx 12V
Idle (floor temp above 110C) - Below 1.5V

Seeing as the connector is disconnected, am I right in thinking that 0V will be going to the ECU which is why the light is still on? If this is right then what I need to do is actually connect the wires sensor side so that it's always getting 12V and so the light goes out. Is my train of thought right?

 

If you're going to try that I would suggest tapping into a switched voltage source as opposed to a constant voltage source.

 

Or just pull out the idiot light cluster go in the back and remove the bulb... did the same thing when deleted the abs on my car.

 

Page 50-22 of the S4 wiring diagram shows the heat hazard switch. The B wire goes to ground, and the B/Y wire is from the ECU. The switch must use some kind of thermistor to adjust voltage depending heat, so why not just jump both sides of the plug together? That should allow the ECU to see constant ~12V. You'd just be removing the source of resistance from the circuit.

 

The FSM (section 4a for na, 4b for turbo) states that jumpering the two wires results in the light coming on.

 

I have never seen that light turn on in either of my FC's. I would say just take the bulb out.

 

Yeah, I thought about it a little more after I posted that, and came to the same conclusion. It's too bad there isn't a diagram of the "switch" itself to show exactly how it works. I guess replacing it or removing the bulb in the warning light cluster may be the best routes.

 

Odd. Book says pull the connector apart (engine running) and to make the light come on, you jumper the two wires in the harness side of the connector. So if you disconnect the plug it seems the light should never come on.

What is the voltage on the B/Y wire in the heat hazard sensors connector with the car idling???? Elect plug apart. Should be close to 12vdc.

Anytime the key is to just ON and the car not idling, then the Hazard light will come on and stay on.

On a normal car if the hazard sensor get hot, then it's swich closes and puts a gnd on that B/Y wire and the hazard light comes on..........cause it's looking for a gnd. What is the voltage on the B/Y wire when the car is idling and the connector is pulled apart? I bet it's real low like 2vdc or less since you say the hazard light comes on when the plug is apart and engine is running.

I've no idea why your car is screwed up. I'd check and make sure the two wires are B/Y and B.