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CMP - Cam shaft Position Sensor

3.2) CMP - Cam shaft Position (sensor)

What is it? This electrical device is very similar in concept to the crank position sensor (above) in that it detects the position of the rotation of a shaft, in this instance the cam shaft. It is the cam shaft signal that indicates to the ECU that cylinder one is at top dead centre at compression and in the process provides the ECU with the timing reference for fuel injection. The cam shaft sensor provides extra information, to that of the crank sensor, to fine tune timed events such as injection and spark delivery.

Where is it located? The location of this device depends on the design and age of engine. On many modern overhead cam shaft engines the cam shaft sensor is located either on the end, or to the side of the end, of the cam shaft housing. On older pushrod engines the cam sensor is found where the distributor would once have been located. This type sensor assembly makes use of the distributor shaft meshing directly, at its bottom end, with a gear on the cam within the engine block. In this respect the distributor shaft is just an extension of the cam shaft. On the top end of this distributor shaft is a magnetic armature. The cam shaft sensor, that measures the movement of this armature, is located in the cover and uses either magnetic or 'Hall effect' pickup modules.

How does it work? The sensor detects the position of a magnet or set of teeth on the gear on the end of the cam. An electrical waveform output signal is sent to the ECU as the cam turns. The cam sensor tells the ECU that cylinder 1 is at TDC on its compression stroke prior to ignition. The cam sensor ensures the correct timing of the fuel injection cycle. If the timing belt ever jumps a tooth on the cam the lack of agreement between the respective signals from the cam and crank sensors is indicated as an error condition by the ECU.

Symptoms of faulty cam sensor

Associated OBD2 error codes DTCs: P0341 - P0349; P1345

  • Hesitant acceleration - miss-timing of fuel injection due to a faulty CMP can cause intermittent loss of power.
  • Starting difficulty/failure. If the faulty CMP timing problems are severe they may cause the engine not fire at all, or to fire and then stall, or stall at some random time without warning.
  • Hot engine stall and failure to restart - Sometimes the fault of the CSS only manifests itself when the engine is hot. Over time thermal stress can cause cracking and can weaken electrical junctions within the CMP. The CMP may work well at cold start up but can then cause a hot running engine to stop with little chance of restart whilst the engine is still hot; once cooled the down the engine may readily restart and again run for a limited period until hot.

Note The cam sensor body often protrudes into the cam shaft gallery and when it's 'o' ring seal becomes age hardened, engine oil may leak back into the sensor electrical socket plug connector causing errors due to interruption of signal.

How to check? It is not technically easy to determine that the CMP is at fault and, like the crank sensor, may require the use of an oscilloscope. If it is part of a sophisticated on board diagnostics system its failure may be logged as a specific error code in the ECU. Due to the variability problems with engine running are often experienced well before any error codes are set by the ECU.

2 pin socket (magnetic - sine wave output). One pin is 'ground' the other is 'signal'. A voltmeter set to 2 volts AC should measure a signal in the 0.2 to 2 volts range on the 'signal' pin.

3 pin socket (Hall effect, magneto - square wave form output). One pin is 'reference' (5volts), one pin is 'ground' and the third pin is 'signal'. A DC voltage should be detectable in the 0.5 to 1.5 volt range from the 'signal' pin.

It is important that the voltage measurement take place at start up when the engine is cold and again, 20 minutes later, when the engine has fully warmed up to operating temperature. Often the voltage output from faulty sensors declines with temperature rise.

How to fix? If the CMP failure is due oil leakage into the electrical connector then a thorough clean and a renewal of the oil seal on the CMP may correct the situation. It can be a wise precaution to change the connecting cable as oil migration beneath the insulation may possibly contaminate components at some distance to the CMP.

If the CMP has an internal fault then it must be replaced.

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2007 Saturn Aura XR 3.6 code p00116. new timing chains and all parts...128,000 miles any ideas besides the crankshaft reluctor.. Car runs great idols smooth

you got a bit carried away with the code
code p 0016 refers to crank shaft position/cam shaft position sensor, bank 1 sensor A---correlation === causes --wiring---CKP sensor --CMP sensor ---mechanical fault
code p 0011 refers to cam shaft (CMP) intake /left /front bank 1 --timing over advanced / system performance==== causes ---valve timing---engine mechanical fault --- CMP actuator ---wiring
you didn't mention the fault so consider this
if the timing is out on the intake cam shaft , it will idle good but play up as the timing actuator moves it further advanced with rpm
if the actuator is not wire properly or the solenoid is faulty , then the inlet will lag with increased rpm and again cause you problems
It is doubtful if the position sensors for either the crank or cam shafts are a problem because it starts and idles good

Nov 12, 2017 | Saturn Cars & Trucks

1 Answer

94 Jeep Grand Cherokee 4 by 4 4.0 6 cylinder intermittently cuts out I know it's the cam position sensor but I've heard there's a way to test it and also how do you clean it

There is really nothing to clean, unless you find sludge on it.

Camshaft Position (CMP) Sensor

OPERATION The Camshaft Position Sensor, or CMP sensor is located inside the distributor. The PCM uses the CMP signal to determine the position of the No. 1 cylinder piston during its power stroke. The PCM uses this information in conjunction with the crankshaft position sensor to determine spark timing among other things.
The CMP sensor contains a Hall effect device which sends either a 0.0 volt or a 5.0 volt signal to the PCM depending on the position of the distributor shaft.
If the cam signal is lost while the engine is running, the PCM will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will not run after it is shut off.

Fig. 1: Exploded view of a common camshaft position sensor and related components-1996 5.2L engine shown

  1. Make sure that the ignition is OFF , remove the distributor cap and turn the engine over by hand.
  2. Verify that the distributor shaft turns. If the distributor shaft does not turn, the engine must be checked for proper mechanical operation.
  3. Backprobe with a high impedance ohmmeter between the CMP sensor connector middle terminal and battery ground.
  4. Verify that the resistance is less than 5 ohms. If the resistance is not as specified, repair or replace the wiring as necessary and continue the test.
  5. With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and either of the end terminals.
  6. Verify that a 5 volt or greater signal is present at one of the two terminals. If not as specified, repair or replace the wiring as necessary and continue the test.
  7. With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and the end terminal that did not have the 5 volt or greater signal.
  8. Crank the engine by hand and verify that the voltage reading alternates between 0.0 or 5.0 volts.
  9. Install the distributor cap and crank the engine with starter. Verify that the voltage reading is 2.5 volts (averaging voltmeters only).
  10. If the voltage readings are not as specified, the sensor may be faulty.


Aug 02, 2017 | Jeep Cars & Trucks

1 Answer

where is cam shaft sensor located on a 08 saturn aura

Which engine ? This vehicle had option of six different engines , 2.4 , 3.5 , 2.8 , 3.0 , 3.2 , 3.6 And are you picking on the right part ? What code > DTC P0010: Intake Camshaft Position (CMP) Actuator Solenoid Control Circuit

DTC P0013: Exhaust Camshaft Position (CMP) Actuator Solenoid Control Circuit
It may not even be a cam sensor problem !
DTC P0340: Intake CMP Sensor Circuit

DTC P0365: Exhaust Camshaft Position (CMP) Sensor Circuit
DTC P0341: Intake Camshaft Position (CMP) Sensor Performance

DTC P0366: Exhaust Camshaft Position (CMP) Sensor Performance
Camshaft Position (CMP) Actuator System
The camshaft position (CMP) actuator system is an electro-hydraulic operated device used for a variety of engine performance and operational enhancements. These enhancements include lower emission output through exhaust gas dilution of the intake charge in the combustion chamber, a broader engine torque range, and improved fuel economy. The CMP actuator system accomplishes this by changing the angle or timing of the camshaft relative to the crankshaft position. The CMP actuator simply allows earlier or later intake and exhaust valve opening during the four stroke engine cycle. The CMP actuator cannot vary the duration of valve opening, or the valve lift.
During engine OFF, engine idling conditions, and engine shutdown, the camshaft actuator is held in the Park position. Internal to the CMP actuator assembly is a return spring and a locking pin. During non-phasing modes of the camshaft, the return spring rotates the camshaft back to the Park position, and the locking pin retains the CMP actuator sprocket to the camshaft

It may

Jul 06, 2016 | 2008 Saturn Aura

1 Answer

03 Chevy 2500HD 6.0 Gas I have no power to the 10A fuse for the crank with the key on or off truck does start. A P0342 code keep coming up

code p0342 refers to cam shaft position (CMP) sensor A bank 1 --low input===causes--wiring short to ground---CMP sensor---ECM
Check for wiring shorting out on the engine /body, replace the cam sensor on bank 1

Jan 31, 2015 | Cars & Trucks

1 Answer

2001 jetta vr6 cranks but won't start have fuel and spark replaced camshaft sensor, new plugs valve cover gasket got code of PO343 and PO740

code po740 refers to torque converter clutch(TCC) solenoid-circuit malfunction==causes --wiring--TCC solenoid-ECM/TCM
code p0343 refers to cam shaft position sensor(CMP) A bank1-high input.==causes --wiring short to positive--CMP sensor---ECM. check which cam sensor you replaced and check the wiring connectors. use a code reader to reset the cpu when finished

Sep 06, 2013 | Volkswagen Jetta Cars & Trucks

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