Duramax Diesels Forum Truck of the Week
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Old 08-08-2018, 11:23 AM
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Johnston11106 Johnston11106 is offline
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Default P0340 Camshaft Position sensor

So this morning driving into work my truck threw the P0340 cam sensor code. The RPM dial was jumping all over the place, however the truck ran fine. It's not knocking. I've read through some posts and most lean towards the sensor itself. How hard of a job is it? The stealership near me quoted $500.

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Old 08-08-2018, 11:32 AM
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Chevy1925 Chevy1925 is offline
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will the truck restart? generally it wont restart after throwing that code if it really is bad.

pull upper fan shroud, pull fan, pull belt, pull fan pulley bracket out and replace sensor.
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Old 08-08-2018, 11:38 AM
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Johnston11106 Johnston11106 is offline
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Quote:
Originally Posted by Chevy1925 View Post
will the truck restart? generally it wont restart after throwing that code if it really is bad.

pull upper fan shroud, pull fan, pull belt, pull fan pulley bracket out and replace sensor.
Yes, it's not restarting at all. I cranked on it a few times and it flashed the CEL and then holds steady with CEL. A couple times it acted like it wanted to turn over completely by I think the ECM is preventing it. Of course all this happens when I dont have the time to fix it.

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Old 08-08-2018, 04:32 PM
Ron Nielson Ron Nielson is offline
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DTC P0340

Camshaft Position (CMP) Sensor Circuit


Circuit/System Description

The hall effect camshaft position (CMP) sensor produces 3 ON/OFF pulses for each revolution of the camshaft. The CMP output is pulse width encoded. The engine control module (ECM) uses the CMP and crankshaft position (CKP) output pulses to determine the engine speed and position. The CMP is connected directly to the ECM by the following circuits:

The 5-volt reference circuit
The low reference circuit
The CMP sensor signal circuit

Conditions for Running the DTC

The ignition is ON.
The engine is turning faster than 50 RPM.
DTC P0340 runs continuously when the above conditions are met.
DTCs P0335, P0336, P0642, or P0643 are not set.

Conditions for Setting the DTC

The ECM does not see a CMP sensor signal for more than 2 seconds.

Action Taken When the DTC Sets

DTC P0340 is a Type A DTC.

Conditions for Clearing the MIL/DTC

DTC P0340 is a Type A DTC.

Diagnostic Aids

If the CMP sensor signal is lost while running, the engine will operate normally. If the CMP sensor signal is not present on start-up, the engine will not start.

Circuit/System Verification

If DTCs P0642 or P0643 are set, diagnose those DTCs first.
Engine running, observe the DTC information with a scan tool. DTC P0340 should not set.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Disconnect the CMP sensor.
Test for less than 1 ohm between low reference circuit terminal 2 on the ECM side of the connector and ground.

If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 on the ECM side of the connector and ground.

If less that the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 1 on the ECM side of the connector and ground.

If less than the specified range, test the affected signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
If greater than the specified range, test the affected signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

Ignition OFF, connect a 3A fused jumper wire to the CMP signal circuit terminal 1 on the ECM side of the connector.
Ignition ON, momentarily touch the end of the fused jumper wire to ground. The CAM signal present and the engine RPM parameters on the scan tool should change.

If the CAM signal present and the engine RPM does not change, replace the ECM.

Ignition OFF, inspect the wiring harness for any damage, opens or shorts.

If the circuits test normal, replace the CMP sensor.
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Old 08-08-2018, 05:40 PM
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Tothemax Tothemax is offline
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check the harness down by the ecm. the harness likes to rub on the inside of the fender liner. I had a lbz same code and it was rubbed and turned green down there
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Old 08-09-2018, 02:51 AM
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Thanks guys, I will look into it

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