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Intermittent Start Issue (won't start if sitting in sun)

Crazy as it sounds I’ve had my mechanic scratching his head for a month over an intermittent issue starting my car. It’s a 1998 Jetta GLX and it won’t start if it gets too hot outside. I drive the car daily, but frequently do not start it until 4 or 5PM. Without fail, if the weather is above 80 degrees, the car will not start. All the dash lights and electronics come up, and it’s like it can’t engage the engine. It doesn’t try to turn over at all. If I wait until after 8PM when it’s cool and the sun is gone, it starts up on the first try without hesitation.

This doesnt’ occur if I’m able to park in a garage for the day OR if there’s no sun OR if the car has been driven earlier in the day…only if it sits in the sun during peak heat.

Anyone ever experience anything like this?

This is a well documented problem on old Honda Accords. The main relay (makes the fuel pump run) is the culprit. It’s under the dash and sees the same temperature as the car interior. I replaced the main relay on my '92 Accord several years ago and fixed the problem. Cost me $50 for the main relay plus my own time (1 hr max).

I know nothing about VWs and the chances that this is your problem. I suggest that you find a VW forum and look around or post your problem there.

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Do you mean car wont crank when you say “it’s like it can’t engage the engine”? In the business we say Motor Turns Over But Will Not Fire

The motor doesn’t turn over at all. The best way I can describe it is as though I’m trying to start the car without the clutch pushed in. The dash lights all go on, but nothing is happening under the hood. I’ve asked the mechanic to check the clutch switch, but he said that looks fine.

I’ll definitely look into this. When your Honda had this problem did it throw a code at all?

Yeah: I believe in the Honda fuel pump relay situation the motor would still turn over but would not fire. Your situation is motor will not turn over.Not the same as the Honda.But now why wont your Jetta crank when ambient is over 80F?.All electrical problems start at the battery,check and report.Correct me if Iam wrong about the crank,no crank about the Honda.

My guess is a bad starter solenoid or possibly relay.

Any component that has coils, and that includes relays, solenoids, and motors, has the coil windings insulated with a thin varnish-like coating. That coating has a different thermal expansion coefficient than the copper it covers, and even though there are bond adhesion tests standard to the industry, as the copper beneath it expands and contracts the coating becomes brittle and cracks. When this happens, the copper when heated and expanded opens up the cracks and the coil windings short out, making the coil ineffective. That makes its component inoperative.

The reason I suspect the motor solenoid first is because its proximity to the motor subjects it to more heat than a component that’s not mounted up against the motor.

Check for 12VDC at the motor assembly terminals when the key is in eth “on” position and the failure is manifesting itself. If you have that, you can bet you need a starter assembly (unless VW’s solenoids are mounted as a seperate unit, which I doubt). If you do not, see if you have a starter relay. It’ll probably be in a relay box under the hood. Start there looking for voltage.

The problem does seem to similar to the problem on Hondas (which is a relay problem).
Try this, the next time it doesn’t start, open the hood a few minuets and let the engine compartment cool. If it then starts, tell your mechanic. If this doesn’t help, open the windows for a few minuets. If it now starts, the problem could be inside the cabin. Again, tell Mr. Mechanic.

I wonder if there is enough room to just jump the solenoid (as a elimination test)

Yep. I’ve done this test, it’s definitely related to the temperature inside the cabin. Any time the issue has occured the cure has been to open all the doors and sunroof and give it 10 minutes or so to air out. For the time being, this means I haven’t been stranded anywhere, but it sure makes 10 minutes seem like forever!

I am having this exact problem on a 2009 Jetta SE, and am desperate to get it fixed. Just as with the original poster, it only happens late in the afternoon after I have allowed my car to sit in direct sunlight for an hour or more. When I turn the key, the ignition doesn’t fire at all. The dashboard lights up as normal, and no error codes are posted. Eventually, after the sun goes down or moves enough to shade the car, it will start with no problem.

Other forums that I belong to have indicated that it could be the Relay 109, which is housed behind the driver’s side dash, and can apparently become overheated by the direct sun beating down on the car. I am going to ask my dealer to replace it, but will also ask them to look at the starter solenoid.

Does anyone know if the original poster’s problem was ever resolved?

Thanks for the post, I’ve been having this issue w/my Honda for the last 2 weeks. Will start every time except when I go to leave at 5pm and it’s blistering FL hot out!!! Something I can check out over the weekend.

I have the same problem with my 98 Toyota Camry except it does it when it’s cold are the sun doesn’t shine. But soon as the sun shines on it, it cranks with no problem??? Someone please give me feed back asap

Ancient thread, different car, and opposite problem. You should start your own thread.



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