SIGNAL FUNCTIONS
The CMP (Camshaft Position) sensor is a Hall Effect type sensor that
generates a digital frequency as windows on the timing disk pass
through its magnetic field. The frequency of the windows
passing by the sensor as well as the width of selected windows
allows the PCM to detect engine speed and position.
Engine Speed - Is determined by counting 24 windows on the
timing sensor disk each camshaft revolution.
Fuel Timing Control - The position of cylinder #1 and #4 is
determined by distinguishing a narrow or wide window in the camshaft
timing sensor disk.
Engine Mode Selection - Allows the PCM to discern when the
engine is in the off, crank or run mode.
Injection Control Pressure - Engine speed is one of the
controlling variables in the calculation of desired injection
control pressure.
Exhaust Back Pressure - Exhaust back pressure control is a
function of the engine speed and load.
Fuel Quantity Control - Engine torque and fuel is controlled
and is dependent on engine speed. Fuel quantity is determined
by engine speed.
FAULT DETECTION MANAGEMENT
An inactive CMP signal during cranking is detectable by the PCM.
An inactive CMP signal will cause a no start condition.
Electrical noise can also be detected by the PCM, if the level is
sufficient to effect engine operation a corresponding fault code
will be set. The engine will not operate without a
functioning CMP signal. The NGS tool will display
a PID value of zero RPM and zero fuel-PW when no CMP signal is
present.
After removing connector always check for
damaged pins, corrosion, loose terminals, etc.
| Connector Checks to Ground (B-) |
| (Check with Sensor Connector Disconnected and
Ignition key off, all accessories off) |
| Test Points |
Spec. |
Comments |
| A to Grd. |
< 5 ohms |
Resistance to chassis ground check with key off, if > than 5
ohms harness is open. |
| B to Grd. |
> 1000 ohms |
Resistance less than 1000 ohms indicates a short to ground. |
| C to Grd. |
> 1000 ohms |
Resistance less than 1000 ohms indicates a short to ground. |
| Connector Voltage Checks |
| (Check with Sensor Connector Disconnected and
Ignition Key on) |
| Test Points |
Spec. |
Comments |
| A to Grd. |
0 - .25 volts |
If greater than .25v signal ground is open or shorted to
VRef or battery. |
| B to Grd. |
5 ± .5 volts |
VRef check key on, VRef not present check open/short to grd,
see VRef circuit |
| C to Grd. |
12 ± 1.5 volts |
If < than 10.5 v check for poor connection, if 0 v check for
open/short to grd circuit. |
| Harness Resistance Checks |
| (Check with breakout box installed on engine
harness only) |
| Test Points |
Spec. |
Comments |
| #65 to A |
< 5 ohms |
Resistance from harness connector to 104 pin connector -
Signal grd (CMP has dedicated grd circuit) |
| #90 to B |
< 5 ohms |
Resistance from harness connector to 104 pin connector - V
Ref. |
| #49 to C |
< 5 ohms |
Resistance from harness connector to 104 pin connector - CMP
signal |
| Test Points |
Operational Voltage Checks |
| (+) #49 to (-) #65 |
(Check with breakout box installed in line with the PCM) |
| Voltage |
Position |
Comments |
| 12 ± 1.5 v |
Vane |
With the breakout box installed, the CMP sensor & PCM
connected, bar engine by hand. |
| 1.5 ± .5 v |
Window |
The CMP signal voltage should change voltage state as timing
wheel on cam is rotated. |
| Diagnostic Trouble Code Description |
| 0344 |
= |
Incorrect number of sync to transition counts detected,
possible intermittent CMP sensor/circuit fault |
| 0341 |
= |
Electrical noise detected, check wire routing and grounds |
| 0340 |
= |
Inactive CMP signal detected during engine cranking when ICP
pressure was sufficient for starting |
|
