DTC 3-1-4

3-1-4 CAMSHAFT POSITION SENSOR SIGNAL




Trouble Code Conditions
For the ECM to tell which cylinder is being supplied with fuel and spark, the Camshaft Position (CMP) sensor is required. The camshaft turns once for every two revolutions of the crankshaft, so the CMP sensor signal is high for one crankshaft revolution and low for the next. If the signal remains either high or low for more than about 25 seconds while engine speed exceeds 810 rpm, Diagnostic Trouble Code (DTC) 3-1-4 is set.

Substitute value(s)
- ECM gives double injection and ignition.

Fault source(s)
Signal too high:
- Signal lead short circuited to live.
- Break in signal lead.
- Break in power lead.
- Break in ground lead.
- Contact resistance in connections.
- Defective CMP sensor.

Signal too low:
- Signal lead short circuited to ground.
- Defective CMP sensor.

Fault symptom(s)
- Poor acceleration.

TEST PROCEDURE




OTHER DTC's
- Read off other DTCs.

If DTC 1-2-3, 4-1-1 (2-4-3), 1-4-3, 4-3-3 and/or 4-1-3 are stored
^ Check CMP sensor, Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Knock Sensor (KS) and EGR-temperature sensor common connector # 30 on ECM for contact resistance, oxidation and break.

If none of the above DTCs are stored:
^ Status report. Proceed to STATUS REPORT section below.




STATUS REPORT
^ Permanent fault, signal too high:
- Proceed to: PERMANENT FAULT, SIGNAL TOO HIGH section below.

^ Permanent fault, signal too low:
- Proceed to: PERMANENT FAULT, SIGNAL TOO LOW section below.

^ Intermittent fault, signal too high:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO HIGH section below.

^ Intermittent fault, signal too low:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO LOW section below.

PERMANENT FAULT, SIGNAL TOO HIGH
Check ground lead
- Ignition off.
- Disconnect CMP sensor.
- Ignition on.



- Connect an ohmmeter between CMP sensor connector contact 1 (to ECM) and ground.

Ohmmeter should read approx. 0 ohms.

If value OK:
^ Check power lead. Proceed to CHECK POWER LEAD section below.

If value differs:
^ Check ECM contact. Proceed to CHECK ECM CONNECTOR section below.




CHECK ECM CONNECTOR
- Ignition off.
- CMP sensor disconnected.
- Check ECM connector for contact resistance and oxidation.
- ECM connected.
- Connect an ohmmeter between CMP sensor connector contact 1 (to ECM) and ground.

Ohmmeter should read approx. 0 ohms.

If value OK:
^ Source of DTC is bad contact in ECM connector.

If value differs:
^ Check lead between CMP sensor contact 1 and ECM # 30 for break.

CHECK POWER LEAD
- Ignition on.
- CMP sensor disconnected.



- Connect a voltmeter between CMP sensor connector contact 3 (to ECM) and ground.

Voltmeter should read battery voltage.

If value OK:
^ Check signal lead. Proceed to CHECK SIGNAL LEAD section below.

If value differs:
^ Check ECM contact. Proceed to CHECK ECM CONNECTOR section below.




CHECK ECM CONNECTOR
- Ignition off.
- CMP sensor disconnected.
- Check ECM connector for contact resistance and oxidation.
- ECM connected.
- Ignition on.
- Connect a voltmeter between CMP sensor connector contact 3 (to ECM) and ground.

Voltmeter should read battery voltage.

If value OK:
^ Source of DTC is bad contact in ECM connector.

If value differs:
^ Check lead between CMP sensor contact 3 and ECM # 10 for break.

CHECK SIGNAL LEAD
- Ignition on.
- CMP sensor disconnected.



- Connect a voltmeter between CMP sensor connector contact 2 (to ECM) and ground.

Voltmeter should read approx. 5 volts.

If value OK:
^ Check CMP sensor. Proceed to CHECK CMP SENSOR section below.

If voltmeter reads less than approx. 5 volts:
^ Check ECM contact. Proceed to CHECK ECM CONNECTOR section below.

If voltmeter reads more than approx. 5 volts:
^ Check lead between CMP sensor contact 2 and ECM # 8 for short circuit to live.

After fixing:
^ Check signal from CMP sensor. Proceed to CHECK SIGNAL FROM CMP SENSOR section below.




CHECK ECM CONNECTOR
- Ignition off.
- CMP sensor disconnected.
- Check ECM connector for contact resistance and oxidation.
- ECM connected.



- Connect an ohmmeter between CMP sensor connector contact 2 (to ECM) and ground.

Ohmmeter should read 0.5 - 3.0 k ohms.

If value OK:
^ Source of DTC is bad contact in ECM connector.

If value differs:
^ Check lead between CMP sensor contact 2 and ECM # 8 for break.




CHECK CMP SENSOR
- Connect CMP sensor.
- Erase DTC.
- Start engine and rev to 1500 rpm.

If no DTC is set:
^ Source of DTC is bad contact in CMP sensor connector and/or ECM connector.
^ Check connectors for contact resistance and oxidation.

If DTC 3-1-4 is set:
^ Test with new CMP sensor.




CHECK SIGNAL FROM CMP SENSOR
CMP sensor can break down as a sequential fault if signal lead is short circuited to live.

Check signal from CMP sensor as below.

- Connect CMP sensor.
- Erase DTC.
- Start engine and rev to 1500 rpm.

If no DTC is set:
^ Source of DTC is bad contact in CMP sensor connector and/or ECM connector.
^ Check connectors for contact resistance and oxidation.

If DTC 3-1-4 is set:
^ Test with new CMP sensor.

PERMANENT FAULT, SIGNAL TOO LOW
Check signal lead
- Ignition off.
- Disconnect CMP sensor.
- Ignition on.



- Connect a voltmeter between contact 2 on connector and ground.

Voltmeter should read approx. 5 volts.

If value OK:
^ Test with new CMP sensor.

If value differs:
^ Check lead between CMP sensor contact 2 and ECM # 6 for short circuit to ground.




INTERMITTENT FAULT, SIGNAL TOO HIGH
Check leads and connectors
- Check CMP sensor and ECM connector for bad contact, contact resistance and oxidation.
- Check lead between CMP sensor contact 1 and ECM # 30 for intermittent break.
- Check lead between CMP sensor contact 3 and ECM # 10 for intermittent break.
- Check lead between CMP sensor contact 2 and ECM # 8 for intermittent break and intermittent short circuit to live.

INTERMITTENT FAULT, SIGNAL TOO LOW
Check leads and connectors
- Check lead between CMP sensor contact 2 and ECM # 8 for intermittent short circuit to ground.