Today: Truck Won't Start on Damp Days

Dear Car Talk

Dear Car Talk | Mar 24, 2014

Dear Tom and Ray:

In January, the water pump went out on my 2001 Dakota (V-6 engine). Everything under the hood got soaked with coolant. I had the water pump and all the hoses replaced, as well as the drive belt. Now when there is very foggy or damp weather and the truck has been sitting for a day or more, it won't start. After a few hours, when the temperature rises a bit and the air moisture is reduced, it will start and run fine. On one occasion, I hit a small puddle in the road, and the engine quit. After about 10 minutes, it started again. Is there a sensor that will cut the engine off if it gets damp? Does the "catalyst system efficiency" have anything to do with this problem? What do I need to replace to fix the problem?

-- Bob

RAY: You need to move to where there's a drought, Bob. Have you considered Death Valley?

TOM: I don't think your problem has anything to do with your water pump failure or the eruption of Old Faithful under the hood that came with it. I think it is a faulty sensor problem.

RAY: My guess would be the crank angle sensor. On your truck, that's located on or around the transmission belt housing, which makes it vulnerable to moisture and splashing water.

TOM: As the name implies, the crank angle sensor measures the position and speed of the crankshaft, and sends that information to the car's computer so that all the elements of combustion in each piston can be timed to happen at the right moment.

RAY: Knowing where the crankshaft is in its revolution allows the fuel to be injected and the spark to be delivered at just the right millisecond. It allows the valves to open and close precisely when they should. And without that information (when the crank angle sensor does not send a signal) the car definitely won't start. Or run.

TOM: You also ask about the catalyst system efficiency, Bob. That tells me that your check-engine light came on, you looked up the trouble code, found out it meant "catalyst system efficiency" and you had no idea what that meant, but the truck was still running so you ignored it. That about right?

RAY: It means your catalytic converter is failing, Bob. That won't produce the symptoms you describe, but when the converter eventually plugs up completely, it will prevent the car from running at all.

TOM: And it'll certainly prevent you from passing your state emissions inspection soon, if it hasn't already.

RAY: So you probably need a crank angle sensor and a catalytic converter, Bob. I'd do the sensor first. That way, you know you'll be able to start the truck on the day you have an appointment to get the converter replaced.

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