# Diagnosing Cam Position Sensor vs. Crank Position Sensor



## groggory (Apr 21, 2003)

I always get the diagnostic procedures for these mixed up. Also, there is a lot of misinformation out there on how to diagnose these right. 

What are the diagnostic steps for each? And what are the symptoms to lead a person to either of these sensors in their search for fixes? 

Thanks! 

From my FAQ: 

# Cam position sensor - normally fails when hot. 
CPS resistance specs (2001 AMU): 
Pin 1 = shielding (at square, keyed end of harness connector) = ECU 108 
Pin 2 = ground = ECU 90 
Pin 3 = signal = ECU 82 
On the sensor, pins 2-3 should read 730-1000 ohms, while pins 1-3 and pins 1-2 should read infinite ohms (no connection) 

# Crank position sensor - normally fails when cold


----------



## groggory (Apr 21, 2003)

If someone would be so kind please chime in if you know something


----------



## herb2k (Jul 29, 2007)

Not sure of the proper technical procedure, but the Crank Position Sensor usually fails when hot (you might notice the car takes longer to turn over on warm starts, or needs multiple tries). 

When the Crank Position Sensor fails entirely, the car will refuse to run, even poorly - whereas the Cam Position Sensor failing would result in poor running.


----------



## KF1.8T (Nov 16, 2011)

When my crank position sensor went-the car would take a long time to turn over and the EPC light was on. It would also jerk randomly when driving, the RPMs would just shoot down and then back up. I haven't had the cam position sensor fixed-but i have had the cam shaft tensioner fixed-that cause rough idle at stops and was expensive.


----------



## Charlie_M (Mar 23, 2011)

groggory said:


> I always get the diagnostic procedures for these mixed up. Also, there is a lot of misinformation out there on how to diagnose these right.
> 
> What are the diagnostic steps for each? And what are the symptoms to lead a person to either of these sensors in their search for fixes?
> 
> ...


 Your FAQ *is* mixed up  Those pin-outs and resistance readings should be for the *crank* position sensor. You took them from my post (here: http://forums.vwvortex.com/showthre...ut-Circuit&p=75688707&viewfull=1#post75688707) Sorry I didn't notice it in the FAQ earlier. 

From one of the SSP publications, the two sensors work together, especially when starting. If you had the crank sensor only, you could still get a TDC signal and thus generate spark at the right times, but you would need 2-3 or more crank revolutions before the signal was locked. By adding the *cam* position sensor, TDC can be determined much quicker, so ignition can be done much quicker too, 1 or 2 crank revolutions usually. 

One of the hallmarks of a bad crank position sensor is seeing no tach reading when cranking over trying to start. 

Edit: Bad idea to use CPS abbreviation, I'm going to spell out cam or crank from now on


----------



## 87vr6 (Jan 17, 2002)

herb2k said:


> When the Crank Position Sensor fails entirely, the car will refuse to run, even poorly - whereas the Cam Position Sensor failing would result in poor running.


 This is how I diagnose them, along with vagcom. 


Without the crank sensor, you won't get spark or fuel, so if you were to remove one coil from the plug, use a screwdriver to arc it out while someone tries to start the car you could tell... No spark=crank sensor, spark, then the crank sensor is good. 


And hopefully if people search and/or read the FAQ/DIY thread that I'm sure this will go in, engine speed sensor and vehicle speed sensor ARE NOT the same, despite repeated idiotic attempts in this forum by people claiming they are. 

Engine speed sensor is the crank sensor on the front (or drivers side on longitudal motors) of the block. 


Vehicle speed sensor is on the transmission and has nothing to do with the motor.


----------



## groggory (Apr 21, 2003)

Just saw that there were updates to this thread....

I updated the FAQ with the updated information.

What do you guys think..



the faq said:


> * Sensors *
> 
> *Cam Position Sensor*
> This is a hall effect sensor that reads a wheel on the end of the intake cam with either 1 or 4 windows (depending on year of car). It sits on the timing belt side of the engine on the intake manifold side.
> ...


----------



## VWAUDITEK (Dec 26, 2006)

If you have a bad cam chain tensioner,you will also get a camshaft advance setpoint not reached and IF the tensioner goes slack and chain jumps a tooth you will get a correlation code for crank & cam sensors,the car will idle bad and rev OK.


----------



## groggory (Apr 21, 2003)

VWAUDITEK said:


> If you have a bad cam chain tensioner,you will also get a camshaft advance setpoint not reached and IF the tensioner goes slack and chain jumps a tooth you will get a correlation code for crank & cam sensors,the car will idle bad and rev OK.


The chain can jump a tooth?!?!?! Eep! I can see that ending poorly. If it can jump 1, it could just as easily jump 12


----------



## groggory (Apr 21, 2003)

VWAUDITEK said:


> If you have a bad cam chain tensioner,you will also get a camshaft advance setpoint not reached and IF the tensioner goes slack and chain jumps a tooth you will get a correlation code for crank & cam sensors,the car will idle bad and rev OK.


Would you mind looking up the exact codes you'd get for those conditions? I'll add them to the faq


----------

