BMW starter troubleshooting and replacement does not have to be hard.
Read on to learn how to quickly test and replace a bad starter the right way.
In this post we will be testing and replacing a starter on a BMW 3 series.
After reading this you will easily be able to….
- Test the starter.
- Know for sure that the starter needs replacing.
- Properly install the new starter.
- Enjoy the job
First rule out the obvious.
- Battery charged?
- Are there any loose battery connections?
- Any immobilizer or other codes?
- Blown fuses etc.
Is it the starter? Let’s be 100% sure.
Check the ground strap from the engine to the body. These straps corrode over time and fail. Without this ground the vehicle will not crank over at all.
Many people forget that a strong ground is just as important as power when it comes to electricity.
You can send all the amps you want to a starter motor, it will never work unless the ground is strong enough to provide a “path” for that amperage?
You can guess, install a new starter and find the problem is not fixed.
Or you can do it right…..
I choose right, you still with me….. ? Good.
I’ve had shops send cars to us after giving up on fixing them.
After doing all kinds of diagnoses for a no start. parts changing, and guessing.
They waste a ton of time and money because they don’t test the basics first. All this, just to find out the ground was bad.
The first thing I do before anything else on these beemers is run a external ground. This will quickly determine if we have a broken ground strap.
There will be times when you do this and it starts right up.
This will especially look good to your customer if they come for a second opinion and you confirm they do not need the starter that shop xyz tried selling them.
Create a solid ground between the engine and the chassis. Be sure to use a beefy jumper cable.
Try to crank it over.
If the starter engages it’s the ground. Just try it a few times to be sure.
Find the ground strap that is broken. The grounds are located in different locations depending on the year.
Still no start? no worries, lets move on.
Scoots got some tricks up his sleeve…….
There is a way to access the starter signal wire fairly quickly.
Looking at the engine, on the passenger side there is a cover for main junction points. The crank signal wire is located in this box, it is easier to get to for testing rather than trying to get to the starter itself.
It is the fatter white wire, as seen here…
Once we have access to the correct wire, we use our power probe to tap in, we can now see if the starter activation signal is present while cranking.
Have another person try to crank the car over while you watch the power probe.
If you have battery voltage at this wire while cranking the starter signal is good. This confirms that the starter is being told to crank the engine over.
Now we have checked our ground and signal to the starter, the last thing to confirm is main power to the starter motor. This is the feed wire that sends the big amperage to the motor.
I use a long screwdriver to touch the lug on the starter motor and then use a power probe to check voltage.
If all of these grounds and voltages are correct its time to get to work replacing that starter.
Great, so now it’s time to replace the starter assembly, we have a good diagnoses and the authorization from the customer. The very first thing to do here is disconnect the battery.
It’s located on the rear passenger side of the trunk behind the side cover.
The starter assembly is under the intake manifold, you will need intake gaskets, throttle body gasket, starter, and new starter bolts.
One thing to note. There are PCV breather hoses under the intake as well. These become brittle over time and break very easy.
You need to remove them, if you are a weekend DIY er I would suggest getting them all, If one breaks you are SOL until you get a new hose.
The dealer should be able to let you know what hoses are needed under the intake, some models are different.
We have everything we need so lets get to work. Remove the air box and the front air duct first, make sure you put something in any open points of intake…….. unless you want to find out the hard way where that nut you dropped went. No need blowing a motor over something stupid, yeah I have seen some crazy things happen over the years, trust me it happens to the best of us.
Completely remove the intake manifold.
To do this you will have to remove the throttle body and fuel feed line. Then unbolt the power steering reservoir and bracket.
Then disconnect the PCV breather hose to the valve cover, these do break a ton no matter how careful you are, they become very brittle, like eggshells. Hopefully they come off easy …….
Once you have all of this disconnected you will need to remove a few more PCV lines and electrical connectors underneath the intake.
There is a bracket directly under where the throttle body was that holds a bunch of wiring. Unbolt the bracket, it should be held on by two t 25 or t 27 torx screws.
Pay attention here and get any other components disconnected from the intake.
Ok, lets pull off this intake!
Take off all of the intake nuts, they are 11 mm.
Then pull back the intake. Pull it back enough to inspect, make sure everything is disconnected first.
Once you are confident everything attached to the intake is off, pull that sucker out! The first thing to do next is stuff rags into the ports on the cylinder head.
You do not want anything getting in there or a starter will be the least of your problems!
You will now see the starter and the big fat white signal wire plugged in to it. Pretty cool how we did not have to check our signal here all the way down here isn’t it ?
Now simply unbolt the starter, one bolt is short and comes from the front. The other is longer, this one is from the back through the transmission.
It can be a little bit of a cramp but you will get it. The bolts need to be replaced. They are stretch bolts. This means they are one time use angle torque bolts.
The bolts are inverted torx heads. You can use a standard box wrench most of the time.
Use flex head gear wrenches to get at the rear bolt if possible.
It’s out! Great work, now lets clean up that mating surface. Remember the starter relies on the ground to the bell housing, the cleaner the better.
I use an angle die grinder with a abrasive “cookie” style disk to clean up the aluminum.
The next step I always do on any starter that takes a bit of work to install is a bench test. This ensures the starter you are installing is good to go.
Bench testing the starter
This is quick and simple, just hook up a battery or jumper pack. The positive end goes to the main power lug and the ground goes to the body of the starter where it bolts to the bell housing.
You want to use a starter button to send power from the positive terminal to the trigger of the starter solenoid. You can jump the terminals with a screwdriver as well.
Ground it, give it main power, send power signal to solenoid. If the starter gives you the old “click… whhheeee” you are good to go.
Fit the starter in and install the NEW bolts. The bolts are one time use.
Replace the starter bolts and torque properly.
The specifications are as follows… these specs pertain to the …
- N 52 / N 52K / N 51 / N 53 engines
- Starter motor mounting to crankcase for the “long bolt” = 20 NM jointing torque + 180 degrees.
- Starter motor mounting to crankcase for the “short bolt” = 20 NM jointing torque + 90 degrees.
- The main power lug to starter torque is 13 NM
The starter is installed and torqued properly, awesome job!
The job is done right if you followed the torques.
All we need to do is install new intake and throttle body gaskets, reassemble the engine in the reverse order. Use silicone spray on all of the PCV hose connections and button it up.
Hook up your battery and crank it up! Road test it and write it up …. this one is done.
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