For 1990-2009 cars
Cell 20: Ignition System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The camshaft position (CMP) sensor is located in the distributor and consists of a signal generator (a hall element and magnet) and a signal rotor. As the signal rotor turns, a magnetic flux from the magnet is applied to the hall element repeatedly. The hall element generates a voltage that is proportional to the magnetic flux. This voltage signal is wave-shaped and is modified into a digital pulse by the comparator and sent to the PCM. The PCM uses this 4 pulse/revolution signal to determine the engine speed and the position of each cylinder. The PCM uses this signal to control the fuel injectors and the ignition timing.

### Conditions for Setting the DTC

No signal from the CMP sensor for 3 seconds with the PCM receiving an engine start signal.

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn off after three consecutive drive cycles without a fault present.

• | A DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

### Diagnostic Aids

Check for any of the following conditions:

• | If a DTC P1500 Starter Signal Circuit is set, diagnose P1500 first.

• | If no problem is found with the CMP sensor or the circuitry, check the CMP sensor signal rotor for proper alignment or damage.

An intermittent malfunction may be caused by a fault in the CMP sensor circuit. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals.

• | Improper mating of terminals.

• | Broken electrical connector locks.

• | Improperly formed or damaged terminals.

• | Faulty terminal to wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, splices, or terminals.

If the DTC P0340 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions since the DTC was first set.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The Powertrain (OBD) System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Determine if a fault is present. Review the Freeze Frame data to determine when the DTC set. Always record this information.

3. Line up one of the signal rotors with the hall element by turning the crankshaft until one of the rotors are in the proper position.

4. Move the crankshaft just enough so that the signal rotor is not in line with the hall element.

5. The CMP sensor is not serviced separately. Refer to distributor service in Engine Electrical for CMP sensor replacement.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition, leaving the engine OFF.
2. Perform the scan tool Clear DTC Information function.
3. Operate the vehicle within the Freeze Frame conditions as noted. Crank the engine if the vehicle will not start.

Does the scan tool indicate a DTC P0340?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition.
2. Disconnect the distributor electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage from terminal 2 to ground (harness side), using a DMM.

Is the voltage at the specified value?

B+

Go to Step 4

Go to Step 7

4 | Probe the distributor connector terminal 1 (harness side) with a test lamp connected to B+. Did the test lamp illuminate? | -- | Go to Step 5 | Go to Step 8
5 |

1. Turn OFF the ignition.
2. Reconnect the distributor electrical connector.
3. Remove the distributor cap, the rotor and the cover.
4. Backprobe the CMP sensor signal circuit at the PCM with the DMM.
5. Rotate the crankshaft so that one of the four signal rotors, on the distributor, are lined up with the hall element (magnet).
6. Turn ON the ignition, leaving the engine OFF.

Is the voltage between the specified value?

3 to 5 volts

Go to Step 6

Go to Step 9

6 |

1. Leave the DMM connected.
2. Rotate the crankshaft so that one of the four signal rotors are not lined up with the hall element.

Is the voltage between the specified value?

0 to 1 volt

Go to Step 11

Go to Step 9

7 | Repair the open in the CMP ignition feed circuit between the CMP sensor and the main relay. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 12 | --
8 | Repair the open in the CMP ground circuit or faulty ground connection. Repair as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 12 | --
9 |

1. Check for an open or a short in the CMP sensor signal circuit between the CMP sensor and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 10

10 | Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement . Is the action complete? | -- | Go to Step 12 | --
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 12 | --
12 |

1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to the Applicable DTC Table

System OK