DTC P0340 Camshaft Position (CMP) Sensor Circuit. Geo Metro 1997

For 1990-2009 cars only

Makes 🢒 Geo 🢒 1997 🢒 Metro 🢒 DTC 🢒 DTC P0340 Camshaft Position (CMP) Sensor Circuit

Circuit Description

The powertrain control module (PCM) receives voltage pulses from the camshaft position (CMP) sensor. The PCM uses these pulses as reference signals indicating engine speed and number 1 cylinder identification. The CMP sensor generates the voltage pulses from the rotation of the distributor shaft. A signal rotor, which rotates with the distributor shaft, passes through the air gap of the CMP sensor. The movement of the signal rotor through the air gap creates a flux in the magnetic field generated by the CMP sensor. The CMP sensor responds to the change in the magnetic field and sends this information to the PCM.

Conditions for Setting the DTC

•	No signal from the CMP sensor while cranking the engine.

•	The condition present for 2 seconds.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL).

•	The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

•	The MIL turns OFF after three consecutively passing trips without a fault present.

•	A History DTC clears after 40 consecutive warm-up cycles without a fault.

•	Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC.

Diagnostic Aids

Check for any of the following conditions:

•	Check for a DTC P1500 Starter Signal Circuit and if found, diagnosis the DTC P1500 first. A starter motor that fails to operate normally may set a DTC P0340. Check the starter motor and starter motor circuits if a DTC P0340 is set and there are problems with the operation of the starter motor.

•	Check the CMP sensor signal rotor for proper alignment and damage. Refer to Engine Electrical.

•	Check for faulty electrical connections at the PCM and circuit components.

•	Inspect the wiring harness for damage or electrical faults.

For proper electrical circuit repair procedures, refer to Wiring Repairs.

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

Test Description

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

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.

This step determines if fault is present.

The CMP sensor resistance can range from 185 ohms to 325 ohms at -10° to 100°C (14° to 212°F).

This step checks the CMP sensor for the correct air gap.

Step

Action

Values

Yes

Did you perform the Powertrain On-Board Diagnostic System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Turn ON the ignition, leaving the engine OFF.
Clear the scan tool information.
Operate the vehicle within Freeze Frame conditions as specified. 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

Turn OFF the ignition.
Check the vehicle at ambient temperature.
Disconnect the distributor electrical connector.
Measure the resistance of the CMP sensor (distributor side) with a DMM.

Is the resistance within the specified value?

185 to 275 ohms at -10° to 50°C (14° to 122°F)

Go to Step 4

Go to Step 11

Measure the A/C voltage from the CMP sensor (distributor side) with the DMM, while cranking the engine.

Is the voltage within the specified value?

0.10-0.40 volts

Go to Step 5

Go to Step 8

Turn OFF the ignition.
Reconnect the distributor electrical connector.
Disconnect the PCM electrical connectors.
Measure the A/C voltage from the ignition reference high signal circuit and the ignition reference low signal circuit with the DMM, while cranking the engine.

Is the voltage within the specified value?

0.10-0.40 volts

Go to Step 10

Go to Step 6

Check for any of the following conditions:

•	An open in the ignition reference high or low signal circuits

•	A short to ground in the ignition reference high or low signal circuits.

•	A short to voltage in the ignition reference high or low signal circuits.

Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 13

Go to Step 7

Repair the faulty electrical connection at the distributor.

Is the action complete?

Go to Step 13

Check the CMP sensor air gap. Refer to Distributor Overhaul in Engine Electrical.

Is the CMP sensor air gap within the specified value?

0.2 to 0.4 mm (0.008 to 0.016 in)

Go to Step 11

Go to Step 9

Adjust the CMP sensor air gap. Refer to Distributor Overhaul in Engine Electrical.

Does the engine start and run?

Go to Step 13

Go to Step 11

Check for a faulty connection at the PCM.
Repair as necessary.

Was a repair necessary?

Go to Step 13

Go to Step 12

Replace the CMP sensor. Refer to Distributor Overhaul in Engine Electrical.

Is the action complete?

Go to Step 13

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

Go to Step 13

Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
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