Replacing a Camshaft Position Sensor

Your "Check Engine" light went on, you read the computer code, and it told you there was a problem with the camshaft position sensor. Perhaps after a little research, or after talking with a mechanic, you panicked a little because, you found, this code might mean you need a new timing chain— a big, expensive job.

This is pretty much what I encountered. But then I called another mechanic to get a second opinion. He said he'd been working on BMWs for fifteen years and never had call to replace a timing chain... more than likely it was just a bad sensor. In any event, it was worth replacing the sensor first. It was a lot cheaper. If that didn't make the problem go away, he advised, then yes, I might have to replace the timing chain. But this wasn't likely.

So I looked at the Bentley manual a little more, talked to some other BMW devotees, probed quite a bit under the hood, and found that, to remove and replace the camshaft position sensor, I'd have to remove the upper intake manifold. I found the directions for this in the manual to be quite sparce and ambiguous on some details. Perhaps this is due to differences in model years. Maybe they assume you should already know the details or that you should be able to figure them out yourself. So to fill the gap, I'll provide a lot more detail here. Before jumping on the job, read through this entire article and occasionally have a peek under your own hood.

Figure 1. Seen from the front of the car. At the bottom of this photo is the fan shroud and the oil filler cap (A) is top left. The easy-to-see end of the camshaft position sensor (B) is mounted on the front of the engine block. The cable from this end leads into a plastic guide (C). Note the small torquoise mark on the cable indicating where the cable enters the guide. This cable takes a left inside the guide and goes down into the darkness (D) where it becomes inaccessible.

On my 1998 318i with a four-cylinder (M44) engine, one end of the camshaft position sensor is mounted on the front of the engine block (see Figure 1) and isn't hard at all to get at. But the other end of the sensor's roughly two-foot cable plugs into a connection block under the upper intake manifold and so, unless this is removed, isn't accessible. Don't fret though. Most anyone who knows their way around tools and who has a bit of patience can do the minimalist version of this job in less than five hours and perhaps as little as one. "Minimalist" here means that we'll be disconnecting the upper intake manifold only enough to get the job done and no more. I'll try to be be clear and detailed enough that it'll be like you've done this job a couple times before.

Parts needed

Figure 2. Gasket for upper air intake manifold. Two are needed.

The five hours allocated for this job doesn't include buying the parts. You never know how long it takes for automobile parts, especially imported auto parts. It might take an hour. It might take three weeks. Who can say? It's possible that at least some of them will need to be special ordered. Unless he already knows your vehicle, your auto parts supplier may ask you for the last seven (7) characters of your VIN, so have that handy when you call. If he doesn't ask you, make sure he's ordering the right parts. Double-check the part numbers from another source. Life's too short to wait for parts which you'll only have to take back and reorder. I've always gotten good results and good prices ordering BMW parts online (computer parts are another story), so you may want to consider that avenue.

Here's what you'll need:

• A camshaft position sensor of course. Your local or online parts store might call it a "camshaft speed sensor".
• A rubber O-ring for it.
• Two steel air intake manifold gaskets. See Figure 2 (right). These are identical and will go above and below the flange which sits right under the upper air intake manifold.
• You might want to get an extra plastic cable guide. Theoretically, you should be able to use the one that's already there. But the plastic may have become brittle with time and heat and so may break even with careful handling. This part is mounted up front and is easy to get at, so you can always get one and mount it later if it comes to that. Then, too, you could also try gluing it back together. I tried Duco Plastic Model® Cement to glue the pieces back together, but it didn't hold. So just to move on, I decided to spend the three bucks for a new one.

Tools

You'll need a set of small metric wrenches, sizes 10mm through 13mm. As usual, a rachet and sockets set help the job go faster and minimizes bloody knuckles. For some inexplicable reason, I found that a seven-sixteenths (7/16") box-end wrench to be the best tool for removing the most inaccessible of the intake's mounting bolts (E in Figure 4). A wide straight-edge screwdriver will be used to loosen a worm clamp (C in Figure 4). And we'll be using a wire coathanger or other stiff wire for fishing, so you'll need pliers and side-cutters to bend and cut it. The camshaft position sensor itself is mounted with an Allen bolt, so you'll need a small Allen wrench. A small flashlight is a must for peering around the innards. Because so many electrical problems are the result of dirty connections, I always keep contact cleaner around. I sprayed the contacts on the connection box end of the new sensor just prior to plugging it in. You might want to do that too. There's not much sense in doing this much work only to have your efforts fail due to a dirty contact, something that could have been remedied in a few seconds with a couple shots of aerosol.

Though I know I should have, I didn't use a torque wrench. (My brother-in-law walked off with mine and I haven't gotten around to buying a new one yet.) It's important, though, to tighten bolts to spec. You don't want your engine shaking loose and dropping parts because a bolt wasn't tight enough. Nor do you want to break off a bolt or strip threads due to overtightening. There's a lot of engineering that goes into assessing relative tensile strengths and differences in expansion and contraction due to heat and cooling of different components. Don't dis all this good science. If you don't already have torque wrench, buy or borrow one. My brother-in-law has one. Ask him.

I used a quart flask of engine oil to prop up the detached upper air intake manifold and so to give me more room to work. Anything about the same height and which won't scratch aluminum should work as well.

At the very end of the job, when you reconnect the battery, two or three things may happen. One is that your car alarm, if you have one, will go off. So you'll want to have the remote handy to put it back into a quiet, usable state. The procedures for doing that are beyond the scope of this document, so you'll have to figure out that part of the job separately. The second and third things that will happen is that your radio/tape/CD player will need to have its security code programmed back into it and the date and time display on the dashboard will need to be set. In your loose time find this code and manual and have these handy at end of the job. Have the computer code resetter also. You'll need it to reinitialize the computer.

For easier reference, here's an itemized list of the tools mentioned above:

• Metric wrenches, sizes 10mm through 13mm. A quarter-inch drive and sockets of the same size can be used on some, but not all, of the nuts and bolts we'll be addressing.
• Seven-sixteenths box end wrench.
• Fat and wide straight-edge screwdriver, suitable for loosening a worm clamp. See Figure (C) in Figure 4.
• Wire coathanger.
• Pliers and side-cutters suitable for bending and cutting the coathanger.
• Small Allen wrench. (Why do they almost never have the size stamped on these?)
• Small flashlight.
• Contact cleaner (optional, but smart).
• Plastic quart flask of oil. This may be an empty. Or you could use something else about the same height. For propping up the upper intake manifold while it's removed.
• Torque wrench.
• A couple clean rags. Yeah, your hands might get greasy on this job.
• Car alarm remote and instructions for resetting it.
• Radio/tape/CD player security code.
• BMW Owner's manual for instructions on setting console date and time.
• Computer code reader/resetter.

No electricity

Figure 3. After removing the tray in the trunk, the battery can be disconnected.

The first step to this job is to disconnect the battery. We'll be pushing things around under the hood and playing with electrical components and you never know what kind of wire might hit ground and fry something. It takes just a minute to disconnect the hot side of the battery and that's a small price for peace of mind. Just so there's no excuses, here's how.

To access the battery, open the trunk and remove the black plastic tray on the passenger side by pressing the thumb-sized tab in the middle of it. Gently wiggle it out and set it aside. To avoid getting a shock from handling the battery, make sure you're not standing in a puddle of water, touching a metal surface of your car, or are grounded in some other way. Use a 13mm wrench to loosen the bolt on the red cable until it'll slip off the battery post. Use something like a clean, dry rag to keep the cable from accidently making contact the battery. In Figure 3, you'll see my battery has a red plastic flap attached to it which can be folded down to keep anything from accidentally making contact with the hot. Nice little feature.

Disconnect the accessible end of the sensor

Grab your small Allen wrenches, find the camshaft position sensor on the very front of the engine block (farthest from the windshield). See (B) in Figure 1. Crank out its mounting bolt. Right next to this, also mounted on the front of the engine block, is a plastic guide which holds the sensor cable and a hose. Remove the hose and unscrew the bolt from the engine block. As this guide may be quite brittle, carefully remove the sensor cable from it. Set the guide, its bolt, and the wrench aside for now.

Cut off and discard the overly twisted part of the coathanger and bend the leftover part straight. It should be at least two foot long. (That's .6m in the modern measurement system, or, in ancient measurement, as long as your arm.) Bend a small hook into one end of it and clamp it lightly, not tightly, around the sensor's cable just below the plastic head. Set this aside for now. We'll come back to it later.

Removing the upper air intake manifold

This isn't going to be nearly as difficult as you may be thinking. There's only three bolts and two nuts you'll have to lay hands on and all but one of them are easy enough to get to that you can use your rachet on them. The one in the back— closest to the windshield— is the one you'll need to use the seven-sixteenths wrench on. Consult Figure 4 if you can't find all five of these.

As a general rule, I like to loosen all nuts and bolts together gradually. By this I mean that I start at the edges of a component, loosening the outermost nuts or bolts just a little, and move gradually towards the nuts and bolts in center, loosening each of these just a little. When I've loosened all of them just a tad, just enough to ensure that they'll come out without use of a breaker bar, then I go back to the outermost nuts or bolts and loosen these a little more, again moving gradually towards the center again. This helps in a couple ways. First, completely removing each nut or bolt can increase the pressure on the last one(s), making it or them more difficult to crank out and possibly leading to stripped threads or a broken bolt and then the need to use an easy out. Using the gradual method will lessen the possibility of these minor disasters. Second, if something like this does happen— and it always happens with the last bolt I'm trying to get out— I know it before I have the assembly 99% taken apart, so can put it back and, hopefully drive down to the parts store and get another one. Note that it isn't necessary to completely remove the front- and rearmost mounting bolts. Just loosen them up enough that they don't grab on the mounting brackets, so the manifold can be lifted up.

Before attempting to lift the manifold though, pull off the small black vacuum hose attached to the front of the manifold and loosen the worm clamp holding the soft rubber boot to the throttle housing closest to the air filter. (See (B) and (C) in Figure 4, below.) Now you can lift the manifold straight up, free it from the two guide bolts, and hang it on the hood rubber just in front of the windshield, or, standing the oil flask on the rearmost of the valve cover, prop it on top of that.

Figure 4. In this photo, to make it more apparent, the upper intake manifold has been gold-plated (digitally). This assembly must be lifted several inches in order to access the camshaft position sensor, whose visible end can be seen at (A). Before lifting, pull off the vacuum hose at (B) and loosen the worm clamp at (C) so the rubber boot can be pulled off. Bolts at (D) and (E) are cradled in mounting brackets and need only be loosened. A long bolt at (F) and nuts at (G) and another, not visible in this photo but pointed to by (H), all need to be removed.

Remove and replace the camshaft position sensor

Now you'll be able to see and get to the hidden end of the camshaft position sensor. Consult Figure 5 because there's two plugs there and there's no sense pulling out the wrong one. You may also want to shake the other end of the sensor cable, the coathanger end, to check that your sensor plugs in the same place as mine. You should see a silvery metal retaining clip holding onto three sides of the socket. Quite unlike vehicles of lesser value, this simple clip is a minor marvel of engineering and doesn't have to be removed. Simply pressing and holding in the side of the clip closest to the windshield will unlock the plug from the socket and allow it to be pulled out. I might be loony, or maybe it's because I've worked on too many non-BMWs, or perhaps the former is a result of the latter, but I can't help but admire the refined design of this clip. Other cars have what are commonly called "Jesus clips". The name comes from the fact that you have to struggle endlessly with five different tools to pry them loose at which time they go flying off into some dark, unknown recess of the engine compartment or the far corner of the garage, never to be seen again, and all you can say is, "Jesus #%@*&!" True, BMWs cost a bit more, but encountering a piece of pleasure like this clip every once in awhile makes it worthwhile.

Figure 5. Peering over the valve cover from the passenger side we can finally see the hidden end of the camshaft position sensor (A) revealed after the upper intake manifold (partially seen in topmost part of photo) has been lifted up. To remove the position sensor plug from its socket, reach a finger behind the plug and lightly depress the clip (the top portion of which is pointed to by B), i.e., push it towards the front of the car (in the direction of the green arrow).

Before pulling the plug out however, bend the coathanger into a big semi-circle and bend a right-angle handle into the non-hooked end. This coathanger then will allow you to steer the front end of the sensor as you tug gently on the sensor cable's plug end and jiggle and poke the coathanger into that darkness under the lower intake manifold, past all the hoses and wires and whatever else is there, and up to where the socket is.

Once you've got the hooked end of the coathanger all the way up to the socket, pull the old sensor out of the socket, remove the other end of the old sensor from the coathanger, attach the same end of the new sensor to the coathanger, plug the other end of the new sensor into the socket— first spraying both the plug and socket with contact cleaner— and then gently wiggle and pull on the handle end of the coathanger to bring the new sensor cable up to the front of the engine near to where it needs to be plugged in.

Before installing the front end of the sensor into the engine block, lay the cable into the plastic guide. There should be a green or blue stripe on the cable which marks where to start. This dot should be visible just outside the part of the guide closest to the sensor end of the sensor cable. See (C) in Figure 1. This done, screw the guide back onto the engine block.

Put the new rubber O-ring on the sensor, dab some oil on it to make it slip in easily, and use the Allen bolt to mount the sensor into place. The Bentley BMW Manual doesn't give the tightening torque for the four-cylinder engine, so I'm guessing it's the same as for the six-cylinder: 5 Nm (3.5 ft-lb). With the new camshaft position sensor now installed, the next step is to put the upper intake manifold back.

Put the upper intake manifold back

Well, we can't just screw it back on now. First we have to replace two steel gaskets, one above the flange, the other below. Gaskets, as most anyone knows, are used to create a good seal between two surfaces which would otherwise leak. Since these they can't be reused and we've taken off the upper manifold, these gaskets should be replaced.

Figure 6. Here the upper intake manifold (A) has been removed to reveal the flange (B) immediately below it. Gaskets on top of and underneath the flange need to be replaced. Resting the heretofore hidden mounting bolt (C) on the engine compartment's seal (right in front of the windshield), doesn't allow enough space to remove the flange though. This is where you need the oil flask.

Place your new gaskets nearby so you can reach each with one hand while your other hand is holding the work. Remove the first steel gasket under the upper intake manifold (see (B) in Figure 6), then remove the flange under that gasket, then the gasket under the flange. You might have to do a little gentle wrestling and wiggling to remove the flange from the bolts protruding from the lower intake manifold, but with patience it can be done without damaging anything. Once you've removed the second gasket, replace it with a new one. With the two mounting bolts and the guide protruding, there's only one way for the gasket to go on. It'll be obvious to you. After the lower gasket is in place, slip the flange back into place, and set in the upper gasket. Now the upper intake manifold can be put back where it was meant to be. Before bolting down the manifold, take a look at the rearmost and frontmost mounting bolts to make sure that they're both fully seated and that the washers on each are in contact with the bolt heads and not inside the mounting brackets.

Start by threading on the nuts and bolts just hand-tight. Then, performing the reverse of the gradual procedure you used to remove them, begin cranking down the nuts and bolts in the center first and move toward the perimeter of the work, i.e., the two bolts on the front and rear mounting brackets. Then return to the center and tighten the two nuts and one bolt to spec with the torque wrench. The tightening torque for all of these nuts and bolts is specified as 15 Nm (11 ft-lb).

Shimmy the rubber boot back onto the throttle housing and tighten the worm clamp holding it in place. Reattach the vacuum hose back onto the manifold. With your car alarm remote near at hand, reconnect the battery. Then reset the car alarm. Finally, re-initialize the computer and, if necessary, recode the radio/tape/cassette player and set the date and time on the console. The manual for your code reader/resetter will have instructions for the former, and your car's owner's manual will have instructions for the latter. The absence of the "Check Engine" light on the instrument cluster should tell you you've fixed the problem. After re-initializing the computer you can read the codes and get this information again. If all's well, I'd recommend going for a short drive. A little jaunt makes sure that everything's running like it should and stretches out the satisfaction of having done the job yourself. Enjoy.