In this blog post we go over code P0340 for the Camshaft Position Sensor error. This could be from either mechanical or electrical issues which we breakdown below.
Your check engine light comes on. You scan your Subaru and see P0340 – Camshaft Position Sensor Circuit Malfunction. That sounds complicated, but don’t panic. The basic idea is pretty simple: your Subaru’s computer is having trouble getting the signal it expects from the camshaft position sensor. This could be from either mechanical or electrical issues.
First Question: What Changed?
Before you start buying parts, ask yourself: What changed right before the P0340 code appeared?
Did you:
- Replace the camshaft position sensor?
- Work on the engine?
- Replace a timing belt or timing components?
- Unplug connectors?
- Change the engine wiring harness?
- Do an engine swap?
- Replace another sensor or part nearby?
If the car worked fine before you changed something, start by checking the area you just worked on. It’s easy to bump a connector, pinch a wire, or forget to fully plug something back in.
Check the Electrical Components
One of the easiest places to start is the camshaft position sensor plug. iWire sells replacement plugs for this sensor (see below).
Find the camshaft sensor and inspect its electrical connector. Look for a connector that isn't fully plugged in, broken plastic or a broken locking tab, bent terminals, corrosion/dirt, or damaged, cut, burnt or broken wires.
If everything looks good to your eyeball, then check the connector with a multimeter or do a pin drag test to make sure everything is working as expected electronically.
A sensor can be perfectly good, but if its electrical connection is bad, the ECU may not be able to see its signal.
It Could Be Grounding
Grounding issues can cause all kinds of strange electrical problems in a Subaru, including camshaft position sensor codes that make it look like the sensor itself has failed. The engine computer relies on a clean, stable electrical ground to accurately read the camshaft sensor signal, and excessive resistance at the battery ground, engine ground, or chassis ground can distort that signal enough to trigger a fault code. Corrosion, loose ground bolts, damaged ground straps, or paint and debris between grounding surfaces can all create this kind of problem.
Before replacing a camshaft sensor, it is worth checking the main engine and battery grounds, cleaning the mounting surfaces, and performing a voltage-drop test to make sure the ECU and sensors have a solid electrical reference. We also recommend improving your grounding system in your Subaru with our Grounding Kit.
Don't Assume the Sensor Is Bad
P0340 has the words "Camshaft Position Sensor" in its description, so it's tempting to immediately replace the sensor. But the sensor isn't always the problem.
If you already replaced the camshaft sensor and P0340 is still there, stop replacing sensors and start looking elsewhere.
Check the Mechanical Components
The camshaft sensor needs something to "read" as the engine spins. Depending on the Subaru engine, the sensor reads features associated with the camshaft or cam gear so the ECU can figure out the camshaft's position. Imagine a bicycle gear with teeth all the way around it. Now imagine one of those teeth is missing or damaged. Damaged teeth on the cam gear or crank gear are one of the most overlooked issues that results in a P0340 code.
Also make sure the timing components are installed correctly like the timing belt/chain, crankshaft gear, camshaft gear, pulleys, and tensioner.
iWire Camshaft Sensor Connectors
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