I'm getting the code 2-4-3, "Throttle position sensor signal outside voltage range" on my 850. The lambda warning light comes on, and I have cleared the code a couple of times only to find out that it returns after a couple of days.

Yesterday I removed the top cover to the throttle body and (I think) located the sensor and cables. I cleaned the connector with some WD-40 and plugged it in and out a couple of times. Cleared the code, and thought that was it... Wrong! It came back this morning! :(

I'm not sure what to do. Is it just the sensor, or is it the cables? What does "outside voltage range" mean? Voltage too high? Too low? Bad sensor? I'm clueless. I'd rather not just change the sensor to find out it is the cables or something else!

Would be grateful for any advice.

Stefan

Thank you very much for your replies.

I talked to a Volvo mechanic yesterday, he thought it was the sensor that needed replacement, they tend to shortcut he said. So I'll go for a new sensor.

Now, another question... :)

Is it an easy DIY job? I've got the Haynes manual, and it doesn't look to difficult in the book, but I guess they disassembled everything. If I can do it myself, I'll buy a sensor from a company who have them much cheaper.

Again, thanks!

/ Stefan

I think it's an easy fix for a DIYer. The computer supplies 5 volts to the sensor as a reference. With the throttle closed, you should be able to measure about 0.5 volts, increasing to about 4.2 volts at WOT. These voltages should be measured using a digital VOM and pin leads (I use safety pins) pushed into two of the three wires comming off the sensor, with the key on and the engine not running. Not sure which color wire is positive/negative, but this should be readily apparent when you do the checking. For the 850, I do not believe there is any adjustment - this info is just for checking to see if the TPS is w/in spec.

Here's my question to the group:

I just replaced one on 92 Ford Van with a 351 V8 (hey it's in the family now, right?). A popular modification to increase power is to adjust the TPS (which has just about the same voltage specs as the 850) so that at the closed position, the voltage is as close to 1.0 as possible withoout going over. This usually requires filing out the mounting holes with something like a round chain saw file in order to allow more adjustment. The theory is that this will allow the engine to get into its fuel maps sooner and thus make more power. I've done it and can attest that it does make the engine a little more responsive. Has anyone done this to the 850?

The throttle position sensor (TPS) is a rheostat. It is supplied w/ a voltage that the computer uses as a reference. As the throttle is opened, the rheostat causes the electrical resistance to change, which in turn causes the voltage to change (remember Ohm's Law: V=IR, where I equals current). So, the computer continuously gets a changing voltage which it uses to determine the position of the throttle. However, the computer knows the lowest and highest voltages should be, so if the returned voltage is out of range it throws a code. I think you need to replace your TPS. You can verify this by back-probing with a digital VOM and checking the voltage at idle and the wide open positions (key on, engine not running) and comparing those readings to the specs. Also (don't need the specs for this) you can check that the resistance changes smoothly as the throttle is opened (key off). In my experience, when the TPS goes out, there will not be a smooth change in resistance as the throttle is opened - it will suddenly change.

The TPS on my ’95 850 failed at about 50k miles. The failure mode manifested as sporadic shifting at constant freeway speeds and loads. Removal and probing with a DVM indicated a discontinuous voltage (resistance) reading that got worse with temperature soak. Replacement solved the problem. Interestingly there were NO OBDII codes. The resistance readings were always within spec; the computer was interpreting the faulty readings as an erratic right foot and tried to compensate as best it could.

Kind of reminded me of HAL in 2001…