What this code means
P0340 may indicate that the engine control module is not receiving the camshaft position signal it expects.
What the vehicle may do
- The vehicle may crank longer than normal.
- The engine may run with reduced power commanded.
- The vehicle may show camshaft timing or synchronization-related symptoms.
Possible fault areas
- Possible camshaft position sensor circuit issue
- Possible low reference or reference-voltage issue
- Possible signal wire, terminal, or connector issue
- Possible control module side circuit issue
- Possible mechanical camshaft signal, reluctor, oil condition, or timing drive condition
Diagnostic path
Opening and code logic
On this Silverado, P0340 is a camshaft position sensor circuit code. In plain language, the engine control module may not be seeing the camshaft signal it expects. The truck may crank longer, and when the fault sets, the camshaft position actuator is commanded to park position and reduced engine power may be commanded. Broadly, the possible fault areas are the cam sensor signal path, low reference, reference voltage, connectors, the control module side of the circuit, or mechanical cam signal conditions. Treat the running conditions as monitor gates. The module is looking at starter state, engine running state, crankshaft synchronization, and airflow; one gate includes MAF Sensor = Greater than 3 g/s. P0340 sets when the cam signal is missing or not producing enough pulses: Camshaft Position Sensor = No Signal — For greater than 5.5 s, Camshaft Position Sensor = No Signal — For greater than 4 s — Starter is engaged, or Camshaft Position Sensor = Less than 4 pulse(s) — For greater than 3 s. Other no-signal checks can also be part of the same monitor logic, so use the scan data to decide whether the signal is actually present and stable.
Start with verification before circuit testing
Before diving into circuit testing, start with the basic system checks, then follow a structured diagnostic approach so you are not chasing the cam code before a broader vehicle or shared-system issue is ruled out. With the ignition on and the vehicle in service mode, first make sure the shared reference faults called out by this path are not active. If those are present, check that reference circuit issue first, because it can affect more than just the cam sensor. Then run the engine and make sure the companion camshaft performance fault is not active. If it is active, go to the circuit and system testing path. If it is not active, compare Engine Speed to Desired Idle Speed. If actual engine speed does not equal desired idle speed, move into circuit and system testing. If it does match, look at the scan tool Camshaft Position Sensor parameter and confirm it increments — RPM. If it does not increment, go to circuit testing. If it does increment, wiggle the harnesses and connectors at the B23 Camshaft Position Sensor, K20 Engine Control Module, and X154 Inline Harness Connector while watching that same parameter. If the parameter drops out or does not increment during the wiggle test, repair the wiring, terminals, or electrical connectors as needed. If the parameter continues to increment, reproduce the operating conditions for the code, or reproduce the captured conditions from the failure data, and verify P0340 does not reset. If it stays gone, do not force a repair. If it resets, continue into circuit testing.
Low reference circuit check
For circuit testing, power the ignition and all vehicle systems off. Before doing ground or low reference continuity checks, give the vehicle time to shut down; it may take up to 2 min before the test is accurate. Disconnect the B23 Camshaft Position Sensor connector. Test the Low Reference circuit terminal 2 to ground and look for less than 10 Ω. If it is 10 Ω or greater, disconnect the K20 Engine Control Module connector and test continuity from Low Reference circuit terminal 2 at the component harness to the other end of the circuit at the control module harness. That should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance in that circuit. If the circuit is less than 2 Ω, the path points to the K20 Engine Control Module.
5 V reference circuit check
If the low reference test is less than 10 Ω, turn the ignition on with the vehicle in service mode and test the 5 V Reference circuit terminal 1 to ground. The expected reading is 4.8 to 5.2 V. If it is less than 4.8 V, turn the ignition off, disconnect the K20 Engine Control Module, and test 5 V Reference circuit terminal 1 at the component harness to ground for infinite resistance. If it is not infinite resistance, repair the short to ground. If it is infinite resistance, check continuity from that same terminal at the component harness to the other end at the control module harness; it should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance. If it is less than 2 Ω, the path points to the K20 Engine Control Module. If the 5 V reference reading is greater than 5.2 V, turn the ignition off, disconnect the K20 Engine Control Module, turn the ignition back on in service mode, and test 5 V Reference circuit terminal 1 at the component harness to ground. It should be less than 1 V. If it is 1 V or greater, repair the short to voltage. If it is less than 1 V, the path points to the K20 Engine Control Module.
Signal circuit check
If the 5 V reference is between 4.8 and 5.2 V, move to the Signal circuit terminal 3 and test it to ground. The expected reading is also 4.8 to 5.2 V. If the signal circuit is less than 4.8 V, turn the ignition off, disconnect the K20 Engine Control Module, and test Signal circuit terminal 3 at the component harness to ground for infinite resistance. If it is not infinite resistance, repair the short to ground. If it is infinite resistance, test continuity from Signal circuit terminal 3 at the component harness to the other end of the circuit at the control module harness. That should be less than 2 Ω. If it is 2 Ω or greater, repair the open or high resistance. If it is less than 2 Ω, the path points to the K20 Engine Control Module. If the signal circuit is greater than 5.2 V, turn the ignition off, disconnect the K20 Engine Control Module, turn the ignition on in service mode, and test Signal circuit terminal 3 at the component harness to ground. It should be less than 1 V. If it is 1 V or greater, repair the short to voltage. If it is less than 1 V, the path points to the K20 Engine Control Module.
Sensor and mechanical condition checks
If both the 5 V reference and the signal circuit are in range, check whether the companion camshaft performance fault is present. If it is present, do not skip the physical checks. Look for cam sensor and reluctor problems such as excessive play, foreign material between the parts, incorrect air gap, incorrect installation, looseness, or visible damage. Also check for dirty or contaminated engine oil, and inspect the timing drive and tensioner area for visible damage or wear. Repair or replace as necessary when one of those conditions is found. If those conditions are not found, the path has you test or replace the B23 Camshaft Position Sensor. If the companion camshaft performance fault is not present at this point, the path also has you test or replace the B23 Camshaft Position Sensor.
Repair verification and takeaway
After the repair is complete, keep verification separate from testing: verify the repair and confirm the code stays gone under the proper operating conditions. Takeaway: prove the cam signal, low reference, and reference-voltage paths before condemning a component, and use the scan data and wiggle test to catch connector or harness faults that only fail intermittently. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0340 is often diagnosed by proving the signal circuit, reference circuit, low reference, connector integrity, and related mechanical signal conditions before making a repair decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
