marrahm

Car: 1998 Audi A4Q 1.8T w/ 100K miles
Problem: Won't start unless a coil is grounded first.
Story: Had the dreaded dead cyl 2. Replaced module with Autozone part and replaced all coil packs and plugs at the same time. Car ran fine for a month or so. Now it won't start w/o pulling a coil and grounding it to the block first. Then it will start and you can pop the coil back on.

Autozone replacement part is a Hitachi module that has the Audi PN of : 8D0905351. It was not an exact match to the old one, b/c it mounted only with a different set of holes that were in the filter cover, not the same pair that the stock module used. But car ran fine for a month or so with the module. I threw out the old module, so I can't compare now.

Any thoughts on diagnostics? And what is the difference b/w the Audi PNs of 4A0-, 4D0- and 8D0 (all ending with 0905351) -- if its an important difference, any idea which is the correct one for my car?

thanks,
mike

Ertman

Get a scan of codes

marrahm

Forgot to mention that, sorry.

It threw a code for the dead cyc 2 that was resolved upon replacing everthing.

The shop that had the car for the last month (not a dealership) said it threw a code for a defective cam sensor, but when they replaced that part, neither the code nor the start error were resolved.

I have an ebay cable on order that should let me read the codes directly.

In the meantime, anyone have any ideas about the ICM part numbers?

Thanks,
mike

Yippers®

99.5 shows using an 8D0

marrahm

Ok, using the OBDII reader borrowed from Autozone (not a VAG, but seemed to read codes fine), I'm getting a P0116 coolant sensor error. Is it possible that the engine just won't start if that sensor is bad?

And the problem only seems to happen when the engine is cold. If I ground one coil and start the engine (and reattach the coil while running), she runs fine and will restart fine within a few hours.

Once she sits overnight, however, I have to repeat the grounding process to get things rolling again.


thanks,
mike

Ertman

coolant sensor is $15, rep[lace it and check back with us

marrahm

Believe it or not, a bad coolant sensor can prevent your 1.8t from cold starting. don't know how or why, but I've replaced the sensor (it was a blue top unit) with the dark green sensor from the dealer. At $35 it seemed like a cheap option. Car starts right up and isn't throwing any codes. Interestingly, it would not start with the sensor not soaking in the antifreeze. I tried swapping them out and starting the car before I finished installing just to check it out. Wouldn't work. finished installing the sensor and away she goes.
mike