2004 C70 Transmission jolts, MVSOLVED bad ground

justinwerner · Post by **justinwerner** » 12 Jan 2014, 17:08

While completely stopped at a traffic light the automatic transmission seems to switch to neutral and then drop back into gear. The result is something along lines of feeling like the car behind me bumped my bumper. For a select few reasons, I think the problem is electrical and the onboard computer is resetting itself due to a voltage drop. No engine off dash lights come on, and it never happens while moving. The radio will intermittently shut off (go black) and come back on, (no memory loss). Sometimes in conjunction with the jolt, sometimes while just cruising along. The dash lights flicker at idle but stop with revs. The headlights will dim with a draw (like pulling up on a window switch on a closed window). My gut says replace the voltage regulator. The battery charges fine and shows no sign of weakness. The car has 194,000 miles and has most original equipment. Thanks in advance.

Post by **kcodyjr** » 12 Jan 2014, 19:05

If that has the 5-speed transmission, and I think it does, they did deliberately take themselves out of gear at stops. This was later removed with a software update, because it eats transmissions.

If it feels like you're getting a jolt, I'd expect your upper and/or lower torque mounts are worn as well.

Also sounds like your alternator might be getting weak, and you may have a loose wire behind the radio.

Plug an old school needle style voltmeter into the cig lighter and watch it out of the corner of your eye.

I miss real gauges...

Post by **JRL** » 12 Jan 2014, 19:43

That was only 2001's besides the light/radio deal states he has a short somewhere

Post by **kcodyjr** » 12 Jan 2014, 23:16

Oh? Sorry.

Unless some idiot swapped in an older TCM that hadn't been updated. Long shot there.

Still sounds like he has bad rubber somewhere if the car is jolting.

And I still miss real gauges. Without giving precision readings, they give clues what's happening.

justinswerner · Post by **justinswerner** » 12 May 2014, 16:00

Update.... I replaced the voltage regulator and the car still has the same issue. I can force it to happen the same if there is some major electrical draw. For example trying to put the top down or rolling windows up when they are already up or turning on the highbeams . It will do it on it's own if the AC kicks on. Some dash lights kick on also like the traction control. Is it possible there is a bad relay? People have mentioned a bad ground however. Hitting bumps will not cause it to happen. And often happens when the car sitting perfectly still. Battery checks out fine and charges fine and a hold charge fine. One other note is that the radio will turn off and turn back on at the same time the jolt happens. It still seems as if the car is momentarily powering down and powering back up.

justinswerner · Post by **justinswerner** » 12 May 2014, 16:11

A few other notes... It can happen anytime, in cruise or standing still. The electrical shutoff happens first. The jolt happens because of the power up. It's not the jolt that causes the shutoffs.

Post by **JRL** » 12 May 2014, 16:40

Check ENTIRE electrical system and battery

Post by **precopster** » 12 May 2014, 17:49

Check earths first (easier to find) Undo all the earths in the engine bay and clean the mating surfaces and ring connectors, then move on to other looms.

Check the positive cable for corrosion just prior to the battery. Peel back some sheathing to view.

Post by **abscate** » 13 May 2014, 04:44

When you are done looking for your earths, make a cup of coffee and then check your grounds.

Make a list of all grounds on the circuit diagram and start cleaning them, one by one.

Post by **precopster** » 13 May 2014, 07:31

Earth IS ground: http://en.m.wikipedia.org/wiki/Ground_(electricity)

Makes no difference to me what YOU call it