Temp gauge issue

[jaybird]

Hello fellow Saab owners

I am having and issue with my temperature gauge. I was driving and I looked down and the gauge was reading the line before the red. I immediately pulled over to check the engine and nothing seemed to be wrong. I had no check engine light on. I checked the coolant fill and everything was good. There was no extra pressure in the bottle. I drove the rest of the way home with no issues. I let my car sit overnight to completely cool. When I started my car the next morning from cold the gauge was reading at the first quarter line even at cold. When the car is completely warmed its reading at the top line which is a quarter too much. I also have heat and have noticed nothing wrong with the cooling system. Is this as easy as a temp sending unit?

Thanks for reading, Jason

[9-3 Aero]

Welcome to SaabWorld

The culprit can be a bad contact or wiring Coolant Sensor / Engine Control Unit (ECU), and of course the coolant sensor - which is fairly easy to check. Note the enclosed table, measure sensor resistance at connector pin #1 and -2, and extrapolate values if so needed:

Saab 9-3 MY2005 Coolant Temperature Sensor (T8)

°C (°F)------kohm -----V
-30 (-22) ----26.0 ----approx. 4.73
-10 (-14)------9.4 -----approx. 4.31
0 (32)----------5.9 ----approx. 4.0
20 (68)------- 2.5 -----approx. 3.12
40 (104)------1.8 -----approx. 2.20
60 (140)------0.596 --approx. 1.42
80 (176)------0.323 --approx. 0.89
100 (212)-----0.187 --approx. 0.55

[jaybird]

I replaced the coolant sensor and it is still reading high at the same point on the temp gauge in the dash. The gauge is reading the line just before the red. It normally reads right at half way. No check engine lights are on or anything. When i started from cold after putting in the temp sensor the gauge was already reading at the quarter mark and went up when the car warmed up. The gauge should read all the way at the bottom and come up from there. Could this just be a ECU issue

[9-3 Aero]

Hard to tell. The analogue temperature signal from the sensor is digitalized by the ECU, transmitted on the P-bus to CIM which puts it on the I-bus to MIU, where the needle of the coolant gauge is controlled by a stepping motor. The "bias" now seen could be caused by the process in the ECU, wiring or the stepping motor of course. However is the temperature information used by the ECU for correcting idling speed, controlling radiator fans determinating injection at different phases etc., so if nothing abnormal is seen it may not be the ECU. The stepping motor - tja. Unplug the connector at the sensor, at cold, not running engine, and note any change of the gauge reading .

[CaptainMediocre]

I had an issue with my temp gauge shortly after I bought my car, like less than 24 hours. In my case though the gauge dropped all the way down and stayed there, but the vehicle temp was actually still good and I still had heat in the cabin. I took it into the shop and they replaced the thermostat, charged me 1 hour 20 minutes of labor and the gauge has been working perfectly ever since.

So maybe its possible the thermostat is in play? I'm not sure, just wanted to share what my experience was. At least the thermo is a cheap part.

[gbillows]

Jaybird: I had the same problem, I looked down and the temperature gauge was over the top of the red. I pulled over and everything seemed OK. Also the Turbo gauge has been inaccurate for some time- it always reads above the 3/4 region and always goes into the red when accelerating, although the turbo has always worked fine. When I noticed the temperature gauge today I pulled the car into the garage and turned it off. After several hours with the car sitting in the garage I got into it and the temperature gauge was still in the red even though the car had not been running. I thought it odd that the gauge would register anything with the ignition off, so I removed the fuse (#4 in my 2005 9-3 Arc) and reinserted it when I found it to be OK. Both the temperature gauge and the turbo gauge now work perfectly! I do not know why this would have made any difference- maybe there is a logic board in there somewhere that effectively got "re-booted" when I removed the fuse. Regardless, it saved me a trip to the mechanic (or maybe just postponed it- I will have to see if the problem recurs).

[Tom93]

I have the same problem with my 2005 9-3. I inadvertently discovered when my battery died, the gauge was reset when I reconnected with a fresh battery. Every few weeks the gauge creeps back into the red, and I disconnect the battery for 30 seconds to reset the gauge. This is a pain, so I wouldn't mind some advice on how to reset the computer without disconnecting the battery every time.

P.S.: Pulling out fuse #4 seems to work just as well, and saves me the trouble of popping the hood to disconnect the battery, and then having to reset the clock after I reconnect the battery.

[GlynRB]

My 9-3 Turbo gauges are displaying the same behaviour as stated in this thread. Sometimes the Temp gauge reads ridiculously high, sometimes the Boost gauge does the same, and sometimes (less frequently) the Fuel gauge reads high. Removing and replacing fuse number 4 sorts the problem, but it returns within about a week. Does anyone know of a permanent cure for this strange behaviour?

[swisssaabist]

check battery voltage and ground connections

[Tony.T]

My 9-3 Turbo gauges are displaying the same behaviour as stated in this thread. Sometimes the Temp gauge reads ridiculously high, sometimes the Boost gauge does the same, and sometimes (less frequently) the Fuel gauge reads high. Removing and replacing fuse number 4 sorts the problem, but it returns within about a week. Does anyone know of a permanent cure for this strange behaviour?

Sorry to drag this up from the past but I'm having the same problems. I need to do a reset by disconnecting the battery and the temp sensor for a few hours. This fixes it for a couple of days then off we go again! I'm also looking for a permanent cure! Any Saab specialists near my location?