I've got a totally dead EGR temp sensor. The EGR system seems to have been used only in california, but don't stop reading.

My sensor is shot -reading infinite resistance at all temps (I have a post about rebuilding the EGR vacuum solenoid).
I need to buy a new one as my gas mileage is 18-21 and aggravating and I'd like to finally have the check engine light go away.

The part number is 3517135 and it's been referred to as an engine temp sensor, but this has to be micro-sized to fit inside the EGR valve.

I have a used euro car dealership checking it out for me tomorrow, my enlightening mechanics going to look and I figured, hey if I'm buying used, why not see if someone has one on a totaled car or something? Better to give my money to a brickboarder than a dealership.

My sensor is labeled as being made in W Germany (heh, that's dated) and has the numbers 6268 and 92 12 stamped on it.
-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond

This is the PTC (positive temperature coefficient sensor), as opposed to the later 1992 1/2 NTC (negative temperature coefficient sensor). With a PTC sensor the resistance increases as the temperature increases. One way to confirm it is a PTC sensor is that it has a 1/8 NPTF thread. The NTC is the opposite - as temperature increases resistance decreases - NTC sensors have a M10X1.25 thread - the difference in thread was intentional by Volvo so that people would not mix the sensors up since they require different ECUs and ICU EZK units. This PTC sensor is nearly impossible to find and NTC sensors are currently easily available.

We need to find a way to repair these early PTC (positive temperature coefficient) sensors ourselves. PTC thermistors of a variety of types are apparently manufactured, and theoretically we could open up the bad sensor and drop in a new $5 thermistor then reseal it.

I am currently searching for the same sensor or a replacement thermistor. My 1991 240 has a chronic 4-1-3 EGR sensor temp. warning and I am in the process of understanding the EGR system. In 1992 1/2 Volvo upgraded to a NTC sensor (negative temperature coefficient) that uses a different ECU and ICU EZK. I am currently trying to understand if I can update my 1991 to use the 1993 system by swapping the ECU and ICU EZK - the advantage is that the NTC sensors are easily available. So my working theory is that with a 1993 ECU and ICU EZK I could use a NTC sensor and everything would be fine... however, I haven't tried that yet. That is the next thing I'll try if I can't find a functional PTC sensor or replacement thermistor.

Also, someone might ask me why bother with EGR? I'm sick of the check engine light and there is a chance this will need to be smogged in CA in the future, so I'm trying to sort it out in advance.

If anyone reading this has any experience with thermistors, I'm trying to learn more about those and how to repair a broken sensor.

The 92 12 is the date code, which oddly is two years newer than your car. And there is no friggin way that your inoperative EGR system is responsible for lowered gas mileage on a 700 car. It is an added system (as opposed to integral) used to meet CARB standards. When disabled, it will be calibrated like a 49-state engine. You can fool the system by adding a 750-1Kohm resistor (any wattage) between the temp sensor wire and ground. EGR will operate in the warm mode all the time and possibly cause light stumbling when engine is cold.

Yeah, I'll bet you'd like to buy a working sensor for $50.00. My parts vendor does not stock them but they do show a list price of $240.00, friggin OUCH!!!

Mark

I found a used from the Swedish Auto Warehouse for 65$!
Going to buy it this week. Putting in new NGK basic plugs, should work. I'll post an update to this thread.

-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond