2003 1.8T Tiptronic Cranking Issues

[transducerproducer]

110K miles; new battery, all major servicing up to date.

Starts fine if driven within previous 1-2 days and weather is warm. After that or if below about 40 degrees, often requires jumping (but cranks easily once cables connected).

Where to begin diagnoses? Thanks.

THREAD TITLE EDIT: 2003 1.8T Tiptronic Cranking Issues

[JayTheSnork]

I'd suspect a marginally bad cell in the battery.

no other indications come up on the dash, like a battery-shaped light?

[transducerproducer]

No indicators.

Car has been driven less than 2K miles over past year, so I replaced battery with new 790 amp a couple of months ago when issue first appeared thinking it had just sat for too long. No change, except that cold weather is now increasing frequency. Of course, this coincides with needing to use car more frequently.

[Steve in Chicago]

Get the new battery tested, just to rule out the new one being bad.
Get the charging system tested to rule that out.
You might have a small power drain somewhere.

[transducerproducer]

Tested battery...12.39V w/o load; 10.9V under cranking (immediately following about an hour of normal driving).

[transducerproducer]

Charging results are as follows: 14+V with no accessories operating; 13.4 - 14V with all accessories operating.

[transducerproducer]

Current drain w/o load is .01A.

[JayTheSnork]

10 milliamps is about right, iirc. 12.39 volts on the battery seems a bit low for a very new battery - should be closer to 12.75 or so, I think. I'd get the battery tested, as well as the charging system tested, as was suggested earlier.

it is possible that you do not have a good grounding scheme. under the dead pedal is one ground to check. the ground off the battery ought to be checked as well. many of us tried to preclude grounding problems here in concert with audio system upgrades by doing the Big 3 grounding upgrade - info on it can be found in the Mobile Electronics forum.

[ylwagon]

Tested battery...12.39V w/o load; 10.9V under cranking (immediately following about an hour of normal driving).

10.9 Volts while cranking is pretty normal, but what would be more meaningful would be a measurement when it has sat for days, then won't start. Do you measure this at the battery posts? I'd suggest that you put your negative lead on the intake manifold, and the positive lead on the positive battery clamp, and see what the cranking voltage is. Even better, the positive lead on the solenoid's battery terminal will tell you what the starter is actually getting.