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Occasional trouble starting car...
scott in socal - Wednesday, 26 January, 2011, at 6:30:05 pm
So a couple months ago car wouldn't start after about a 1/2 hour drive. Cranked fine and everything, but just would not start. Finally got out and removed the gas cap and put it back on (the only thing I could think to try) and it started right up.

Fast forward to today, and again it failed to start after a short drive. Of course the first thing I do is the gas cap trick, only this time it doesn't work. At least not initially, the car finally started after about four or five tries.

Any ideas on what could be causing this? I'm a little afraid to drive it now for fear of getting stuck somewhere.

Btw, this is on a 2000 Boxster with 100k miles.

Crank Position sensor?
boxster99 - Thursday, 27 January, 2011, at 11:34:03 am
It happened to my S500 when the engine got hot it would not start. Wait a little bit for it to cool down then it started again. Replace the CPS and everything is a OK.
Hope this helps.

Agree...had the same symptom at 110K.
RainyDayGarage - Thursday, 27 January, 2011, at 4:04:02 pm
The car would start fine when cold, but had problems starting after it got warmed up (like after a short drive to get gas).
The problem got progressively worse over the course of a month when it finally died 10 minutes into a drive...did get it restarted after the car cooled down.

Had the crank sensor replaced...no problem since.
Crank position sensor vs camshaft position sensor..
scott in socal - Friday, 28 January, 2011, at 6:13:28 pm
Are these two the same thing? I see there are two camshaft position sensors per engine - is this what you are referring to? Or is the crank position sensor something different? If so, where is it located? And is it easy to replace?

scott in socal
Are these two the same thing? I see there are two camshaft position sensors per engine - is this what you are referring to? Or is the crank position sensor something different? If so, where is it located? And is it easy to replace?


sensor is located directly the right of the crankshaft (flywheel end of the engine). The sensor fits through a hole in the engine casting flange/face to which the transmission housing bolts to. The sensor works with the flywheel which has metal tabs that stand at right angles to the flywheel. At least one tab is missing. This is used to I believe determine engine speed. The other closely spaced tabs are used to measure acceleration of the flywheel from each cylinder's power stroke and to perform among other things misfire determination.

The camshaft position sensor, of which there are two, are located in the heads. One head has its sensor at the front of the engine and the other head has its sensor at the back of the engine. (Each head's exhaust camshaft is driven from the opposite end of the other head.)

The passenger side head has its sensor located at the front of the engine. If you remove the engine access panel in the cabin you should see a black module afixed the head next to a green plug of some material. (I'm looking at a close up pic I have of an X51 engine but the layout's the same for the Boxster engine. Send me a PM with your email address and I'll send you the pics I have of the sensors.)

For the X51 engine I see one bolt ((torx?) holding the sensor in place. (There may be a bolt behind the connector that accepts the wiring harness.)

The other sensor is located on the other head at the back of the engine.

The crankshaft sensor is I believe fairly easy to replace. That is no need to remove the engine or the transmission. But you had better know what you are doing cause if you drop something inside the space between the transmission the engine you'll have to remove the transmission to get the piece out. If you try to start the engine even crank whatever you dropped could cause the flywheel, clutch, tranmission torque converter, transmission housing, even the engine block serious damage.

Before I replaced any sensor -- unless diagnostics clearly indicates the sensor is bad -- I'd try to disconnect the sensor from the harness, then reconnect it. This action will remove any surface corrosion that might have built up between the pins/sockets of the connector. This surface corrosion can affect the signal of the sensor. I fixed an intermittent camshaft position sensor problem in an '96 Mustang GT this way.


MarkW need some help with my care sensor keeps going off the crankshaft sensor when you put the new one on what are you suppose to clean it with before putting it back in?Mercedes.nina3769@gmail.com
MarkW need some help with my care sensor keeps going off the crankshaft sensor when you put the new one on what are you suppose to clean it with before putting it back in?Mercedes.nina3769@gmail.com

The crankshaft sensor should not be that dirty. It will develop a light coating of fine dust but it should not be enough to effect its operation. The "working" part of the sensor detects the blades of the flywheel ring whizzing past and this area of the sensor is located inside the bellhousing and not likely to build up any real load of dirt.

If oil is leaking and coating the sensor this is not good and the sensor needs to be clreaned and the leak addressed.

So what cleaner to use? Automotive parts shops all carry non-residue aerosol cleaning fluid that is safe to use on electrical parts, electrical connections. I'm sure if you are unable ot make a selection just tell the clerk what you want to clean and the clerk can recommend something. I buy this stuff once in a great while but I can't recall the brand name. The stuff wants to be ok to use on electrical wiring and such and it must be residue free.

Be sure the sensor electrical connector and the mating connector on the wiring harness are in good shape. No damage or corrosion.

The sensor mounting may have some adjustment so the sensor can be positioned at the optimum distance from the metal blades. This gap between the sensor and the blades is important but I can't tell you what it should be. This depends upon the model and model year of car you have though I dare say the distance or gap is probably the same over a span of MYs and models.
Re: Occasional trouble starting car...
Alcantera - Thursday, 27 January, 2011, at 4:51:16 pm
I would wonder if your ignition switch is starting to go . Almost all other systems are self checking and would throw a CEL . At 100k your kind of in the needs a new switch realm . cheap to do and your probably due.
turn the key from off to on and the dash lights up like always then turn the key to start and nada.

I have dealt with two no start issues with my Boxster.

The 1st symptom was as I described above. A new ignition switch appeared to correct the problem but the symptom has returned just a very few (less than 3) times and nothing recent, that is I can't remember when it last happened. So long ago I don't even think about it anymore when I start the engine.

Even though the ignition switch was replaced at the same time I had the tech replace the clutch interlock switch and the cruise control disabel switch based on what somenone posted on this clutch switch awhile back I now believe part of the problem is even though the clutch switch is new it may be intermittently bad. Another theory of mine is the position if the switch or the position of that portion of the clutch hardware that contacts the swtich is out of position a bit and the switch isn't being fully closed the time the engine cranks but does not start.

The 2nd time I experienced a no start symptom with my Boxster was when the fuel pump quit. The engine started, ran a bit then died. A restart attempt worked but the engine died just a moment or two after I released the key from start to run. After this, every restart attempt would have the engine crank just fine but the engine gave no signs of any life at all.

There was no fuel smell around the back of the car after these cranking sessions too which gave me a clue that it was the fuel pump. I sort of confirmed it was the fuel pump but the tech at the dealer did his test and based on that and my guidelines replaced the fuel pump which solved the problem.

The various systems (mainly the DME system) is self checking but its behavior if it detects an implausible signal from a critical engine sensor is to simply not trigger any fuel injection pulses and no spark. The engine will crank just fine but it will not run. The engine cranking circuit is a pretty simply and straightforward circuit and the DME can exert little if any control over this.

It doesn't have to because it can and does control spark and fuel.

Anyhow, since fuel is not being injected the engine's exhaust area will not have a fuel smell. This can be mistaken for a fuel pump failure, but there are ways to eliminate the fuel pump.

Since emissions are not affected -- the engine is not running and the DME is not yet in closed loop mode -- the CEL almost certainly will not be turned on and there almost certainly will not be any OBD2 DTCs stored. There might be some Porsche proprietary error codes logged that for instance the DME may flag an error if it receives an implausible signal from say the crankshaft position sensor.


Re: Occasional trouble starting car...
BoxsterBob - San Carlos - Monday, 14 February, 2011, at 5:00:57 pm
I had a similar situation, drive to the store and park, return to the car and the car would crank but not start. I let it sit for 30 minutes and it would start fine. I replaced the sensor - 986.606.112.02 (mine is a 1999) - Porsche Flywheel Reference Mark Sensor, not to be mistaken with the Camshaft Sensors. I bought the part from Vertex Auto for $109 and since replacing it, I have haven't seen the problem.
Re: Occasional trouble starting car...
scott in socal - Monday, 14 February, 2011, at 7:03:26 pm
Yes that is the part I replaced, commonly called the Crank Position Sensor. Seems to have fixed the problem.

Vertex Auto has it now for $134, I got mine new on ebay for $129 no tax and free shipping, so I guess I did okay.
Last summer my car... 2000, 2.7, died in the left hand turn lane awaiting the light to change. It was running fine prior to dying and had been driven about 30 minutes or so. After waiting for almost 2 hours for a flatbed... it finally started after the driver was ready to put hooks on it. It then ran almost the exact same distance and died again as I started to pull away after telling the tow truck driver I was fine and he could leave. I was able to start it by popping the clutch while rolling down hill... not advised but seemed better then the hooks of getting up on the flatbed.

Afterward the car would start from cold and run up to temp and die at idle after 20 minutes or so.

Your experience sounds similar but not exactly the same.

Based on the diagnosis from the board I changed out my crankshaft sensor... and it does seem to have resolved the problem. I have not taken it out beyond a 90 minute drive.

I purchased the sensor from Parts Geek: 2000 Porsche Boxster Crank Position Sensor - W0133-1607897 Bosch - $131.33
Qty Ordered: 1, Qty Shipped: 1.

The removal and replacement wasn't terrible difficult. I posted the process I used about a month or so ago... a little different than what others had suggested, as there was a cable routing holder that I need to get the ratchet and socket between. At some point it became more of a blind removal and replacement. Most of the effort was in getting the car up and secure to remove the right rear wheel... then being able to view the pictures of the engine others had provided and make sense of the sensors location in my mind (something about looking at an engine with the transmission ahead of it messes with my mind). And, the disconnect of the connectors always gives me a little concern not to break something.
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