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DIY Crank Position Sensor (front location)

2020-12-12

How do you know the CPS is bad?

In my scenario, the first symptom was a check engine light (CEL) along with a very bouncy idle. This happened about 5 seconds after start up (after the car had sat for 5 days). (reading the code out gave 1243 - CPS failure 'out of bounds' - search for the 'pedal trick' or 'stomp test' for OBDI cars)

I drove it after that, and a few minutes/miles the CEL went away and the car drove fine.

The next start up  - the engine just cranked and cranked, but finally started. It threw the CEL while cranking, but went away a few seconds after starting. It did this the next few starts, however occasionally it would start fine.

Finally, it just would not start at all. Nothing but cranking. And still throwing the 1243 CEL.

The final end-all-know-all that the CPS is faulty is to measure the resistance withing the sensor, however to do that you have to take it out firstly. Edit you can just disconnect it and test at the connector.

CPS Removal

This DIY says the Intake manifold must be removed, not doing that for a silly sensor.

Searching/posting here on bimmerforums led me to knowing that you can do it w/o pulling the manifold, however it's tough and there is no DIY. 

First Step:
disconnect the battery (always a good start when dealing with electrical)

-you'll need your intake out of the way, and even pull your mass aif flow meter and intake elbow off. This will give you room to get to the CPS's connector. Also remove the radiator cover/alternator ducting.

Second Step:

-Remove fan/fan clutch. If you haven't done this before it's a pain, you sometimes will need a special tool (I always have to use one). Also remember it's reverse threaded. 

Third Step:

-loosen up the fan shroud. This is pretty simple - it's two plastic rivets/clips and you have to disconnect the small coolant hose one the top of the shroud. You don't need to remove the shroud, just move it up a few inches.


Forth Step:

Find the CPS and remove it at the crank. It's just below the tstat housing, slightly on the passenger side of the car. Remove the bolt (5mm Allen wrench).

Then you will need to get the sensor out of the actual hole it's in. I used a small pair of channel locks to twisted it while I pulled it out. Came fairly easily, however some people say this is the most difficult part.


Fifth Step

Removing the wiring to the harness. This was the toughest part for me due to how crammed everthing is. The cable going to the CPS runs under the tstat housing and then above it. It is held into place with a plastic piece which is attached using to C-clips. Read the pelican article, it has a good photo of the piece you need to remove.

Here is that piece removed, you can see how the cable is routed through it. And now removed from the studs.


Sixth Step
Removing the entire CPS from the engine. It should be loose on both ends, but needs to come out. There are a couple things that will help you to remove it. You must remove the engine lift eye, held on with two 13mm bolts.

This should allow you to remove it, and finally test it (you could test it if after disconnecting it if you were really good.

Testing the CPS

According to the bentley, test the resistance between two of the three contacts. Also note, the bentley says look for 1200 ohms, however it really should be closer to 550 ohms.

For sure mine was thd culprit (thank god) (oh and I notice this pic was with the multimeter at 200ohm range, I did test it all the way up to 2000k - nothing measured).


I also had to remove the oil filter to give me a bit more room. Others have said you must remove the banjo fitting for the vanos oil line, however, I did not. It was vert tight though between the oil filter housing and the vanos oil line.


Installation of CPS

The install is pretty much every back wards. The tricky part is to guess where to put the funny plastic clip on the cable. This could be done easily - I would connect the connector first, then using judgement put the plastic piece on the cable, install that piece, the install the CPS. I did mine the other way around and it wasn't that easy.

Another note, the CPS is a tight fit in the hole (I know what you're thinking) I just wiped out the hole and got it a little more than half way down, then started the bolt (so that you make sure the bolt hole is lined up).

The connection point was also difficult to get back onto the metal plate, it really is stressing the wiring harness it feels until it slides in, then it's good.

The bentley also calls for a certain gap between the crank and the sensor, I just put a folded piece of paper between the two to make sure there was a slight gap.

Make sure to remember to install the lift bracket and remember to tighten the coolant hoses.

I did not and it made the first trip after installing well long and wet.

Other than that, it's pretty straight forward. Connect your battery and crank it up. Mine started right away and the 1243 code was gone. It did very briefly to throw a 1281 (ECU voltage) code, but that was due to the battery being disconnected.

Above information is my personal perspectives. I hope it will help.



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