Excessive heat effects on PCM/ECU

Can excessive heat in the engine compartment cause the PCM/ECU to fail?

Here’s a long story made as short as possible.

I purchased a cherry used Saab 93 with only 30,000 miles on it.
i’ve owned Saabs my whole life.

Within three weeks of ownership I was unable to avoid a tread from a tractor trailer lying on the highway.
It took out my spoiler, cowling, and slightly damaged the radiator.
The body shop authorized a radiator replacement.

Within 1 week of getting the car back from the body shop ( in the early spring), the engine would overheat under excessive load.
Hills and such.
So much the the A/C would automatically shut and warn me of the situation.

I took it back to the auto body shop.
They could not duplicate the issue.
Said they couldn’t find anything wrong.
Told me it was likely an “air bubble” and it should work itself out.

About three weeks later the outside temperatures rose significantly.
The car now started overheating constantly.
Once telling me to immediately pull over.
I found that venting the engine heat into the cabin would instantly bring the needle down to safe operating temperatures.

I limped to the body shop.
They had it for two days.
This time replicated the situation, but could not find anything wrong.

They sent it to the local Saab guy.

They duplicated the issue instantly and took all of 5 minutes to isolate the problem.

The body shop had left a cap on the hose.
Actually the cap had worked it’s way inside the hose so that they could attach it to the radiator, but the cap was still inside the hose.
Water did not circulate for 6 weeks.

The body shop accepted responsibility and paid for repairs.
But this engine had only 30,000 miles on it, and I was concerned that thermal stress would manifest itself moving forward.

They have reluctantly agreed to handle any heat related issues.
I told them I wasn’t looking to nickle and dime them, but felt the should bear some responsibility for heat damage.

Low and behold, driving to work this morning – just 10 days since the repair – my PCM/ECU failed.
Car shut off. Done.
Codes indicate the problem is a defective PCM.

So I do a little investigating.
There are not excessive reports of the ECUs on 04 Saab 2.8Ts going bad.

I also learn that one of the biggest reasons they fail is thermal stress causing micro-fractures on the circuit boards.
And it sounds like they may be susceptible to extreme heat.

I have not contacted the body shop yet.
I’d like some input before I do.
I’m not looking to nickle and dime them.

What say you?
Do you think the issue could be caused by thermal stress ?


First of all, how the heck did you find a 93 Saab with only 30K miles on it :wink:

Where is the ECU located? Which side of the firewall? Unless the ECU is located right at the top of the engine compartment and that engine heat would get to it with nothing in between to shield it from engine heat, I’d tend to doubt the radiator cooling problem would be a likely cause. Unless the engine really overheated to the max. And if it did, the ECU is the least of your problems.

It appears you were watching the guage and mitigated the problem by turning on the heater as necessary. In that case, the engine may have slightly overheated, but I don’t see that damaging the ECU.

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Could you tell us whether the radiator fans turn on?
They are supposed to turn on especially when the AC is on but also under normal driving conditions.
My 900’s would in fact stay on for minutes after you turn the ignition off on a hot day.

Indeed, the radiator fans both activated normally. On these newer Saab’s there are two smaller fans. One runs constantly, one runs on demand and will continue after the ignition is off until tempertature is under control.

I was able to mitigate the problem MOST of the time. Two times I received the warning notification to immediately pull over and idle the engine until the temp came down. The first time it went to the shop. The second time I was stuck in a traffic jam on a rather hot day. That time the engine shut off – symptoms of vapor lock. It cranked but would not fire. Thinking it wad heat related I let it sit and cool. It started and ran fine ain 15 - 20 minutes. It was at the shop the next morning.

I missed the mechanic this evening. They are attempting to locate a used PCM/ECU. I was calling to ask where it was located. I know some newer cars locate them in the cabin. I learned they do this because of heat.

The mechanic who quickly diagnosed the body shop’s mistake is Swedish Motors in Marietta, PA. Very experienced with Saab. We discussed likely problems due to heat stress. His main concern was head gasket. He thought I may have avoided serious issues if they have not already manifested themselves, but this makes me a bit nervous.

What else might crop up?

I know, an '04 with 30,000 miles. It was the definitive, “she only drove it to church” car. I fear I may be in for a litany of issues, however.


The ECU is right where it gets hottest, under the plastic engine cover, beside the turbocharger. I’ve been having to get a new one every 40,000 miles. First symptom is going into limp home mode in stop & go traffic / local streets with traffic lights. Looking for a way to keep it cool, maybe add a fan, maybe a rear facing hood scoop or openings. Suggestions?

Steven , you have replied to an 8 year old thread . Look to the right of your screen and you can see the date of last post .

Regardless, looking for information on what people have done to draw heat away from Saab ECUs. Any suggestion where I can find that info or discussion? Thanks!

Since Saab is no longer I guess a Saab Forum if such a thing exists or a good shop that specializes in modifications . I can’t even remember the last time I saw a Saab vehicle .

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Not sure what they were thinking mounting it there. First thing I would try is to see how much slack I could get from the harness to get it as far away from the turbo as possible. Probably require stripping back some of the harness loom. Wouldn’t bother me because if I couldn’t get enough slack, my next move would be the extend the harness. A lot of wires but just repetitive work not rocket science…

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I suggest sending a strongly-worded letter of complaint to Saab.
Oh, that’s right…
Never mind…


What about fabricating a small piece of aluminum heat shield about 1/8" thick and locate it between the ECU and turbocharger? Aluminum absorbs and dissipates heat very quickly. A piece of starter motor heat shield could be epoxied onto the back of the aluminum between the ECU and aluminum shield to prevent any excess heat from reaching the ECU.

Years ago I had issues with Ford TFI module failures caused by heat. I removed the module from the distributor and mounted it inside the air filter housing and extended the pig tail wire harness to reach. Anytime the engine was running the module was cooled by incoming air and there was never a problem with the modules again.

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That will only work if you can get airflow past it. Right now it’s under the beauty cover next to the turbo. Relocating it is necessary unless some rube goldberg setup to bring cool air to it…