DIY engine ground cable replace

[Joshman73]

Had this problem on a 08' 535xi. Went through dealer an indy (about 7 times) with me telling them I must have a bad ground somewhere - won't start after sitting a bit. After I switched out two batteries (the massive $500 ones), 3 alternators, battery cable replacement, and tons hours of f'n around in the engine bay testing and looking, (both shops super reputable in the West Chester PA area), I sent this problem back to the dealer with the note that this is 100% a ground issue and to check every ground on the car (I didn't have access to a spot to work under the car at the time.) They found the ground strap under the vehicle, even though it looked great was not sending the correct ohms that the systems needed and creating a bleed in the car through - if I remember correctly the comfort access system. - Replace those old grounds.

[rhyary]

Originally Posted by roastbeef

Are the exhaust grounds that critical? I always thought they were to get rid of static or something.

Being into ham radio helps to know that grounds are important to electricity and electrical interferences to electronics. These are two different requirements. The electricity that starts your car "travels" in the metal, electricity that creates electrical interferences travels on the surface of metal.

Someone already said so. Grounding is important, but not all groundings are the same.

When prepping a car for ham radio one of the first thing you do is grounding the exhaust in few places and also the hood.

For electrical interferences you use flat copper mash type strap. For grounding the starter type you use a thick copper style strap.

[GORDON.M3]

Originally Posted by roastbeef

Are the exhaust grounds that critical? I always thought they were to get rid of static or something.

Not really cause most aftermarket exhausts don't even have them. The dealer cut mine off when they noticed it was just hanging by the exhaust.

[roastbeef]

Originally Posted by GORDON.M3

Not really cause most aftermarket exhausts don't even have them. The dealer cut mine off when they noticed it was just hanging by the exhaust.

Lol it's one bolt if it was hanging... I doubt it was harder to cut it.

[GORDON.M3]

Originally Posted by roastbeef

Lol it's one bolt if it was hanging... I doubt it was harder to cut it.

I'm not sure why but they snipped it on the end where it was mounted on to the exhaust.

[pbonsalb]

I made new ones for the exhaust out of maybe 10 gauge wire I had.

[ec_E92]

Originally Posted by doogee

For sure!

Mine was the same way but did not solve my starting issue.

BMW is too cheap to insulate these wires like they used to.

Originally Posted by GORDON.M3

A little word of advice, when replacing your ground cable...
Before installing the new one, heat-shrink it with a clear one. protects it from the elements and you can still see if it corrodes.

Can I suggest you DO NOT heat shrink or insulate the ground strap? BMW is not "being cheap" here. It is a flat braided weave for a reason, mainly for flexibility from engine vibration and corrosion resistance. If you insulate it (not sure how you're going to heatshrink flat cable) it will become rigid and then the terminal ends will eventually fatigue and fail. Also, through capillary action, water will wick inside the insulation and rot the cable. The braid allows water to drain through the cable. It's a $40 part that takes 15 min to swap, just do it every 100k and you're good :

[pbonsalb]

Mine came apart at 90k miles. The uncovered flat ground is good, but insulated round cable will last pretty long. Just put a slight S bend in it for vibration or flex.

[GORDON.M3]

Originally Posted by ec_E92

Can I suggest you DO NOT heat shrink or insulate the ground strap? BMW is not "being cheap" here. It is a flat braided weave for a reason, mainly for flexibility from engine vibration and corrosion resistance. If you insulate it (not sure how you're going to heatshrink flat cable) it will become rigid and then the terminal ends will eventually fatigue and fail. Also, through capillary action, water will wick inside the insulation and rot the cable. The braid allows water to drain through the cable. It's a $40 part that takes 15 min to swap, just do it every 100k and you're good :

If your engine is flexing that much then you have bigger problems then a ground cable.

Don't use a very stiff heatshield. You can easily buy a very thin one which won't change much of the flexibility characteristics.

Also to mention, don't fully seal it. When I meant heat shielding it, I meant using a slightly oversized one which kind of protects it from the elements.

The better option is to use a different cable completely, one from an audio store which has gold contacts and slightly over length.

Sorry but the OEM ground cables don't even last 40k miles in some cases. My exhaust ones were cut off after 25k miles.

[mvolps22]

Sorry to hijack...my car will periodically not start and the brake pedal gets so stiff you can't depress it, in my opinion leading the car to not start since it doesn't register the brake pedal being pushed. I bought a new brake vacuum line and sensor that I'll install this weekend but could it be the starter ground? Can't say I've ever pushed the start button 10 times but usually when it doesn't start I just have to let it sit and try again in 30 minutes.

The other symptoms are similar, car will come on and everything is normal but no cranking from the starter.

[Redd]

Originally Posted by mvolps22

Sorry to hijack...my car will periodically not start and the brake pedal gets so stiff you can't depress it, in my opinion leading the car to not start since it doesn't register the brake pedal being pushed. I bought a new brake vacuum line and sensor that I'll install this weekend but could it be the starter ground? Can't say I've ever pushed the start button 10 times but usually when it doesn't start I just have to let it sit and try again in 30 minutes.

The other symptoms are similar, car will come on and everything is normal but no cranking from the starter.

What error codes are u getting? Brake vac sensor failure results in limp mode and a code. Have you considered it might be the starter?

[mvolps22]

Originally Posted by Redd

What error codes are u getting? Brake vac sensor failure results in limp mode and a code. Have you considered it might be the starter?

No error codes and no limp mode. I didn't correlate a stiff brake pedal to the starter but I have no idea.

[Richbot]

I have been getting intermittent implausible value tstat sensor codes on known good sensors, especially at startup, and idle charging voltage was a little bit low. Time will tell on the codes, but idle voltage went up a few tenths. I'm wondering if a voltage drop during cranking was causing some wacky readings during startup.

Mine didn't fall apart in my hands when it came off or anything, but there were several broken wires in a few of the braids, and it looked a lot like OP's, my car has 133,000 miles and is almost 13 years old.

[manixbuy]

I went through the nightmare of replacing my starter on my '08 335xi only to figure out the ground strap was the problem. I had zero symptoms leading up to no-crank and no-start one morning. I had a few codes: A0B4, A0C1, A0C2, 2E97, 2E7C. Since my battery had charge and jump-starts didn't work, I figured the starter motor went bad after 90k miles. After replacing the starter, you could hear the starter solenoid click, but still no crank. I was about to give up and tow it to a shop when it dawned on me that my ground wire was pretty green and corroded and possibly the issue. To test the theory, I connected a jumper cable from where the ground cable connected to the frame and ran it straight to the starter. Just like that it started!
Lesson learned: keep it simple and check your grounds before taking everything apart lol. Check out what my ground cable looked like. It was green and splitting on the end that connected to the engine side.

[pbonsalb]

You can also use your jumper cables as grounds (instead of as jumpers from the battery) and connect up top under the hood from the engine up chassis. The lifting eye is a good place. Easy, quick test.

[Richbot]

Originally Posted by Richbot

I have been getting intermittent implausible value tstat sensor codes on known good sensors, especially at startup, and idle charging voltage was a little bit low. Time will tell on the codes, but idle voltage went up a few tenths. I'm wondering if a voltage drop during cranking was causing some wacky readings during startup.

Mine didn't fall apart in my hands when it came off or anything, but there were several broken wires in a few of the braids, and it looked a lot like OP's, my car has 133,000 miles and is almost 13 years old.

For what it's worth I haven't gotten another t-stat implausibility code since I swapped this out. Time will tell if it's really fixed the issue for me but fresh grounds can't ever hurt.

[jpan08]

Just ran into this issue after picking up lunch, car (2012MY 82,000 miles) wouldn’t even crank, electrical was fine. Had to get it towed to many house.
Replaced the nearly 10 year old battery and still no cranking.
Read about grounding wires and the starter, but thought I’d take a set of jump cables and connect it from the engine lift point to a ground point under the hood and car started up fine. Now looking around for which grounding cable is broken

[buldogge]

Quick question does anyone know the length (approx.) of the strap, off the top of their head. Looks to be about 10-12" long, max, from the pics.

TIA
-Mark in St. Louis

[patroklai]

Originally Posted by buldogge

Quick question does anyone know the length (approx.) of the strap, off the top of their head. Looks to be about 10-12" long, max, from the pics.

TIA
-Mark in St. Louis

I think I still have my old one around. I'll check if I didn't throw it away. I built my own using 0 gauge wire and it's much sturdier and resilient than the oem.

[buldogge]

Originally Posted by patroklai

I think I still have my old one around. I'll check if I didn't throw it away. I built my own using 0 gauge wire and it's much sturdier and resilient than the oem.

I just used some of the pics in the thread to plot/guess at the length...should be really close to 12".

Decent OE type ground straps are readily available from Standard and AC Delco...so I just grabbed one of those.

I gotta throw it up on the lift anyways, and put the summers back on..so I'll know for sure, then.

Thanks,
-Mark

[JPSurratt2005]

I'm just gonna jump in here and give my resolution to my starting issue just in case anyone might also have the same. I initially thought it was ground strap and after replacing the main one I still had starting issues. I could jump the car with a mobile battery pack and it would fire up every time nice and quick, but of course I was attaching the battery under the hood at the jump location.

So that made me think my issue was somewhere between the battery and front of the car. Well, I removed the battery and noticed a bit of rust along the bottom of the tray, and the main cable that attaches to the terminal (see photo) at the front end of the compartment was rusted pretty bad. When I reached down to check it the rusted nut fell apart. I cleaned up the connector, cut off the rusted lug and re-crimped a new copper lug onto the cable.

So far it's been a month or so and everything is great. Nice quick starts and no more jumping. I'll update here if anything changes.

[M_Torx]

yep victim here of a bad ground it started right up like this thankfully spend no money on a starter or anything at all 🙏🏽