BMW Starter Replacement: How To Test and Replace a BMW Starter
If you own a E90 BMW 3 series there’s a big chance the starter will fail, it’s not really a question of “if” it’s “when. That’s why in this article I will cover how to be sure that the starter in your BMW is bad, and how to replace it yourself.
BMW starter replacement does not have to be hard, this article will show you step by step how to quickly test and replace a bad starter in your BMW the right way.
How To Diagnose and Perform a BMW Starter Replacement.
BMW starter failure is nothing new to shops and BMW owners around the world. The starters on these vehicles fail…and often. Even though these starters do have a high failure rate it’s important to diagnose a BMW no start properly, let’s take some time to go over how to diagnose a BMW starter the right way.
What Are The First Things To Check?
- Is the battery charged?
- Are there any loose battery connections?
- Any immobilizer or other codes?
- Any blown fuses etc.
Above I have listed some obvious things that should be checked before jumping right in, there is one thing however that the average do-it-yourselfer may miss …
Check The Ground Strap Before Anything Else.
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. The tell tale sign is just hearing a “click” when trying to crank your BMW over, this narrows things down greatly to the starter or ground.
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. I have personally seen this over and over again, so much so even if you replace the starter in you BMW, the ground must be checked or you may be stuck with the same issue all over again sooner than later.
Check The Ground, That’s The First Step To Successful BMW Starter Replacement.
I’ve had shops send cars to me 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.
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 BMW starter replacement that shop XYZ tried selling them. This will also go over well with the wife and make you look awesome if you are a weekend mechanic.
How Do You Test For a Bad Ground Before Replacing The Starter.
All you want to do is use a beefy jumper cable and connect the engine to the body, (see above) This creates a known good ground between the engine and the car itself.
Try to crank it over. If the starter engages it’s the ground strap 100% Just try it a few times to be sure. Start looking and find the ground strap that is broken. The grounds are located in different locations depending on the year, usually they are connected to the motor mount arm on the BMW.
Still no start? no worries, lets move on.
I Have A Few Tricks For You, 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 much easier to get to for testing rather than trying to get to the starter itself.
It is the fatter white wire, as seen here…
You will need to remove the cowlings and the connector cover on the passenger side of the engine compartment. When this cover is removed you will see some connectors and the fatter white wire, (as shown above)
Once we have access to the correct wire, we use our power probe to tap in and back probe the signal wire, we can now see if the starter activation signal is present while cranking.
Once you have tapped into the signal wire hook up the power probe, have another person try to crank the car over while you watch the power probe. If, when your helper is trying to crank the car over you have battery voltage at this wire the starter signal is good. This confirms that the starter is being told to crank the engine over, there is a small possibility that this wire is damaged from where you are down to the starter, however this is far less common.
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 use a power probe to check voltage by touching the probe to the screwdriver.
If all of the grounds and voltages are correct it’s 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 we know that’s the problem. The very first thing to do here is disconnect the battery, this will prevent any issues with shorting out the main power feed wire when working.
The Battery Is located on the rear passenger side of the trunk behind the side cover.
What You Will Need To Perform a Successful BMW Starter Replacement.
The starter assembly is under the intake manifold, you will need intake gaskets, throttle body gasket, starter, and new starter bolts. 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 warrior 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.
Replacing a BMW Starter.
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.
1. 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. Disconnect the PCV breather hose to the valve cover, these do break a lot 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.
Once everything is disconnected remove the intake manifold.
Take off all of the intake nuts, they are 11 mm. Pull back the intake manifold, enough to inspect, to make sure everything is disconnected properly. Once you are confident everything attached to the intake is off, pull that sucker out! Then stuff clean 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 ?
Remove The Starter.
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.
Preparing To Install The New Starter.
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.
I always bench test a new starter, this ensures the starter you are installing is good, I have installed new parts that are no good.
How To Bench Test a 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.
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 works you are good to go.
Installing The BMW Starter.
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
This BMW Starter Replacement Went Smooth.
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!
Scoot is a Dad, ASE certified mechanic, and blogger. He has been in the automotive business for over 25 Years.