Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

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.

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.