How do you replace the Crank Position Sensor?

Submitted by	Category	Chassis	Public
Ken K. Yee on 09/07/2004 at 03:35 PM	DIY	W163

How do you replace the Crank Position Sensor?

From dickiegoodman on Shopforum:

Since no one volunteered their expert advice on the crankshaft position sensor (CPS) DIY, here it is...hopefully this will help others with what appears to be a common stalling issue in the ML series.

I check NetStar for PO work (done under warranty) and learned the fuel system mod had been done at 29k (now have 48k). So I figured the stalling issue wasn't that. I may be wrong, the CPS was cheaper place to start!

I give this job a 1 to 1.5 stars (of 5) difficulty, and maybe a 3 stars for patience.

Here it is:

1) Get CPS at dealer, its a VIN specific part. $125 from my local stealer.

2) Tools needed: Socket screwdriver, Good lighting (portable) shop lights, size 8 outside torx socket, maybe a ratchet and extentions depending on your flexibility, magnetic part retrieval tool (skip this at your peril), bath towel, and long sleeve shirt, step stool, blue thread locker (optional)

3) Open hood and remove engine cover, it just pulls off and on

4) Set work light(s) toward back of engine, lighting behind drivers cylinder head

5) Set bath towel on front of ML to kneel on of your knees will die, wearing long sleeve shirt or your wrists will be cut.

6) Climb up on towel and look behind engine from above and right (see picture), finding torx attachment holding your CPS.

7) Remove torx screw and pull out CPS, disconnect one way connector (wiring)

8) Replace with new (leaving wire detached for now)

9) This is the hardest step by far, and requires patience and flexibility. Apply some thread locker and insert screw and start the threads. Tighten with torx on socket screwdriver. This step took about 1/2 hour and numerous dropped screws and retrievals with mag tool.

10) Attach wiring to CPS

11) Reinstall engine cover

12) Clean up tools, towel and lights and everything

13) Drink beer and toast yourself for saving yourself at least $100 and a day of your time dropping off and picking up cars at shop

Hope this helps someone in the community.

From WienerWater on ShopForum:

Had a tech in Vancouver B.C explain how to test your CPS, if it starts to fail. He said connect to an ohm meter, should read a steady 850-1200 ohms. Using an air heat gun, start warming the sensor (not hot, but warm as it's plastic), keeping a steady ohm reading, and it should not change much. Mine started to go up fast to infinity, or just lost a reading. When it cooled down, reading started.
Also, he said if the CPS is suspect, watch the tach needle, as it should not jump when it is in the no start mode of the problem. If the tach needle jumps, it is something else, not the CPS.

ThrillKill on benzworld got a photo of the CPS:

So this must be it

Top view behind the driver side cylinder head:

phoenix44 also suggested this:
You might want to put some gum or something on the end of the tor, dropping the bolt would be a major PITA!!. I think I saw a post where someone had removed the inner fender,(sounds like way too much work) to get at the CPS. Considering the CPS is a fairly common problem, it is too bad that it is in such a hard to reach location. It can be done from up top, you have to basically lie on top of the engine to get at it, and it will probably take a few tries. Remember the engine should be cool, other wise you will get burned.

More from ThrillKill on Benzworld:

Well if you were a good boy like me you listened to your mother and ate your spinach. So you probably have Popeye forearms like myself and would find that trying to do this from the top only would drive you insane. I incorporated both the above and under method and it was fairly easy, in fact screwing in the new torx bolt took about 30 seconds. Excuse the terrible photography.

-Remove engine cover.
-Chuck the wheels and jack up the driver side front of ML with floor jack.
-Remove wheel with 17mm impact socket(or tire tool)
-you are now at this point:

-Remove 6 plastic nuts and inner fender. VERY difficult as it is rather rigid. I found the best method was to get an end point started at one end of the wheel arch and firmly tugging it inch by inch:

-Once this is removed, you can now remove the heat shield (3 screws 2x8mm & 1x10mm):

-Now you have a clear shot to the torx bolt and CPS however due to the tight area there is no room to torque a ratchet or driver:

-I piggybacked 4 extender rods (3 full-length and 1 half-length) and a socket driver. To this I snapped on an E8 Torx socket:

-The hardest part! There is a sweet spot and only one sweet spot to make this work. I jacked around for 40 minutes figuring out the right combo of extenders and places to put this rig in. It's here:

-Best way is to place the socket and one extender on the torx screw from the side and feed the rest of the rig down from the top and then couple them together.

A few nervous turns and shazaam!: Leave the rig there for replacing screw.

-After removing the screw, I eased out the old CPS then pulled it up by the wire to the top:

-I removed the old one(it had rust and corrosion on the contact) and replaced with the new, lowered it back down and fitted it back in (line the screw holes up before you plunge it all the way back in)

- Now unsnap one extender with the Torx socket that is still laying in the engine bay. Stick a little gum(I used Dentyne, your call on this one) in the socket and then the screw with a little thread lock applied.

-You can now hand tighten the screw then snap the rig back together for the final tighten.

From rimasl2 on Benzworld:

I repaired my 2000 ML320 with 92k miles on it by replacing the CPS (Crankshaft Position Sensor) myself.

[photo of CPS]

The symptoms of the car were:
1. Occassionally, the engine would crank, but would not start. If I tried 3 or 4 times or came back 5 minutes later, it would finally start. Eventually, (over about 2 weeks time), the engine would crank but NEVER start. It didn't matter whether the engine was warm or cold.

2. One time the engine stalled while sitting at a traffic light idling. It took about 3 minutes before it would start again, and ran very rough for about 3 miles.

3. OBDII scan showed P0301, P0304 and P0300 (cylinder #1, #4 and random misfires respectively).

From reading the messages on this board, it seemed like the CPS was a candidate for replacement.

I 1st checked for good fuel pressure by simply loosening the fuel line in the engine compartment, WITH THE ENGINE OFF, just enough to feel fuel spurt out and tightened it up again. I did this about 2 minutes after I had turned the engine off. I had only run the engine for about 30 seconds (from a cold start) so that it wasn't hot but there was enough time to pressure the fuel line.

[photo of fuel line in engine compartment]

Replacing the CPs took about 1 hour:

Tools needed:
1. Torx E8 socket. Note though that no one sells an E8 (you can get it at Napa Auto Parts)....therefore, a 1/4" 6-point socket with a 1/4" shaft fits perfectly. You must use a 1/4" shaft socket because a 3/8" shaft socket is too large to get into the small space available between the bolt and the body of the CPS.

2. 1/4" shaft to 3/8" shaft converter.

3. 10" extension bar. The 10" extension is the perfect length on the ML320 because it allows you to clear the engine block and valve cover (see photo below).

4. 3/8" socket wrench.

5. a 1/4" screwdrive type socket wrench is also helpful for putting the bolt back in during re-assembly.

[photo of tools used]

To replace, do the following:
1. remove the wire plug off the CPS. You can feel a little lever/latch on the plug, which when pushed, frees the connector.

2. Place the 1/4" 6-point socket, 1/4"-to-3/8" shaft converter, and 10" extension bar on the bolt head. Do this without the socket wrench attached for easier placement on the bolt because of the limited amount of room (see photo).

[photo of the 1/4" 6-point socket on the CPS bolt and the 10" extension bar extending beyond the engine block
.....view is looking toward the rear of the engine compartment on driver's side of the engine block
.....the valve cover and 3ea. spark plug coils are in the center fore-ground]

3. Then place the 3/8" socket wrench on the extension and remove the bolt.

4. You may have to use some muscle to get the CPS out of the bell housing, then clean the seating area so the new one will sit squarely when it is put in.

5. Place the new CPS in and position it properly.,

5. Use the 1/4" screwdriver socket and 1/4" six-point socket to start the bolt. Use the 10" extension and 3/8" socket to tighten it. DO NOT OVERTIGHTEN.

6. Place the CPS cable back on.

That's it, you're done.....mine fired right up and hasn't had a problem in over 2 weeks. It does seem that the engine was a little rough for the first 2 days or so, but seemed to smooth out nicely. Hopefully this was only the computer re-synchronizing to proper sensor readings from whatever it was receiving before.

Thanks to the forums in general for the info. that led me to this solution.

Here's a URL to another DIY explanation with a few good photos here.

And another DIY at auto-trend: http://autotrend.activeboard.com/index.spark?forumID=91042&p=3&topicID=12850144

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