Author Topic: Temperature sensors for glow plug relay?  (Read 245 times)

dave08

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Temperature sensors for glow plug relay?
« on: 03 December 2018, 10:14:33 AM »
Hello.
Back in October I've started the following post http://www.saabtechtalk.com/forum/index.php?topic=3915.0 but had 0 replies.
Now, that "winter is coming", I am positive that this is a temperature related issue. On cold mornings (bellow 7 degrees C), my 2005 TiD starts perfectly without smoke or rough idle. If the outside temperature gets higher, or the engine has worked, stops, and then I restart after one hour or two, I get smoke and rough idle for a few seconds. So  this is a temperature related issue, as the glow plugs  and relay work fine (and were tested). The instrument cluster temperature gauge works fine, so I'm thinking If there is another temperature sensor that transmits information to the ECU or glow plug relay.
I've seen similar situation where a switch was installed to always activate the glow plugs and solve this. I bet on a sensor.
Any ideas please?
Regards.

carrera

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Re: Temperature sensors for glow plug relay?
« Reply #1 on: 03 December 2018, 07:10:12 PM »
I don't generally "do" diesels, but from your description it seems as though cold start enrichment is operating when it shouldn't, or only partial combustion is taking place (smoke being unburnt fuel).

This is quite possibly a temperature sender. The instrument cluster gets temperature from the radiator, not the engine so it's a different sensor. I' sorry I can't give you more specific advice, at least you have a response to this post and hopefully someone with more knowledge will be along soon.
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #2 on: 04 December 2018, 10:04:59 AM »
Thanks you for the reply!
Yes, the smell if of unburnt diesel. I also believe there's another sensor involved, because it works properly when cold. I wonder what it could be...i'll continue to investigate.
Thanks.

Norfolk Jim

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Re: Temperature sensors for glow plug relay?
« Reply #3 on: 05 December 2018, 12:46:07 PM »
Have you checked the MAP sensor - that does funny things..........
Who said diesels dead - mine goes allriot

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #4 on: 05 December 2018, 02:06:54 PM »
There's been a while since I don't clean it...usually I do it every other year.
I may give it a try, but I'm still betting on a temperature sensor.
Thanks.

carrera

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Re: Temperature sensors for glow plug relay?
« Reply #5 on: 06 December 2018, 11:55:33 PM »
Have you checked the MAP sensor - that does funny things..........

How many connections on the MAP sensor ?  If there are 4, then two of them will probably be for a temperature sensor for the engine ECU
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #6 on: 07 December 2018, 10:05:21 AM »
Actually, as I'm afraid of breaking something, I clean it without disconnecting  the plug  :o
It's part number is a Bosch "0 281 002 845" and what you're saying makes sense.
I had a problem with throttle body a few months ago (actually for years, because the car shaked a lot when turning off), a got the CEL and it was filled of oil. I had to replace it.
Maybe the sensor is build to much dirt because of it to. I'll give it a clean tomorrow and post the results!
Thanks.
« Last Edit: 07 December 2018, 10:07:21 AM by dave08 »

carrera

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Re: Temperature sensors for glow plug relay?
« Reply #7 on: 07 December 2018, 07:43:32 PM »
The number you have identified is the Bosch part number- the component is used on many cars.

There are 4 pins:

1 - Ground
2 - Temperature signal
3 - Power supply, 5V
4 - Pressure signal.

Take a look at the fourth post, there is a graph with expected resistance values

http://forums.linkecu.com/topic/7244-bosch-map-sensor-0281002316/

Now the part number is different,but there's a decent chance the internals will be similar to the one on your Saab.

You will need to be brave enough to remove the terminal connector and test for resistance with a multimeter. Pins 2 and 3 should be the correct ones I think.
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #8 on: 10 December 2018, 10:16:48 AM »
Thanks for the reply!
I cleaned the sensor during the weekend, and I'm glad I did it. Check the picture.
Running much smoother, revving a bit higher at idle as soon as I started it. The real test will be starting the engine at a higher environment temperature than this morning, but even when cold the car is running much better.
I'll let you know.
Thanks.
« Last Edit: 10 December 2018, 10:21:48 AM by dave08 »

Norfolk Jim

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Re: Temperature sensors for glow plug relay?
« Reply #9 on: 10 December 2018, 02:14:10 PM »
Mine only lasted 4 days after I cleaned it so got a new Bosch one for about 40 - Saab wanted over 200!!!!!! Made massive difference but car is now sold for collection on Monday so it had better behave till then
Who said diesels dead - mine goes allriot

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #10 on: 10 December 2018, 02:28:15 PM »
Mine only lasted 4 days after I cleaned it so got a new Bosch one for about 40 - Saab wanted over 200!!!!!! Made massive difference but car is now sold for collection on Monday so it had better behave till then
Actually I've done this last year. I though it would maintain itself clean for longer but...
Yes, they are a lot cheaper ordering them online or through an independent garage.
Thanks.

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #11 on: 11 December 2018, 09:20:26 AM »
...And the real test yesterday. Higher temperature during the afternoon, and still some smoke, not as much as before nor the idle.
Maybe the MAP(or something else) needs a replacement. Probably it can be tested with a tech2?
Thanks

carrera

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Re: Temperature sensors for glow plug relay?
« Reply #12 on: 11 December 2018, 11:23:29 PM »

You will need to be brave enough to remove the terminal connector and test for resistance with a multimeter. Pins 2 and 3 should be the correct ones I think.

Simple multimeter to test the temp sender  ;)
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

dave08

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Re: Temperature sensors for glow plug relay?
« Reply #13 on: 12 December 2018, 10:08:50 AM »
I'll keep investigating. Thanks!
By the way, I believe that the EGR also sends temperature reading to the ECU/Glow plug relay, right ?
It must be one of them ...unless there's still other temperature sensors (not counting with the coolant).
Thanks
« Last Edit: 12 December 2018, 11:00:40 AM by dave08 »