Quick answer
Code P0393 is “Camshaft Position Sensor ‘B’ Circuit High (Bank 2).” The ECM has detected an abnormally high voltage — usually a flat, near-reference signal instead of a healthy pulsing waveform — from the camshaft position sensor designated “B” on Bank 2 (the bank that does not contain cylinder #1). The usual culprits are a loose or oil-contaminated connector, an open or shorted-to-voltage signal wire, or a failed sensor.
The P0393 trouble code points to a high-voltage electrical fault in the Bank 2 camshaft position sensor “B” circuit, which the ECM uses to time fuel and spark. This guide covers the symptoms, causes and fixes for P0393, and shows where a scan tool with live data like the iCarsoft CR Max P reads the cam signal to pinpoint it.
1What Does the P0393 Code Mean?
P0393 is a generic powertrain DTC set when the ECM sees a high or open voltage on the Bank 2 camshaft position sensor “B” signal circuit instead of the normal pulsing waveform. Sensor “B” conventionally refers to the exhaust camshaft sensor; Bank 2 is the cylinder bank without cylinder #1. With no usable cam signal, the ECM falls back on a default timing strategy, which hurts starting and running.
2Symptoms of the P0393 Code
- Check engine light on.
- Hard starting or a long crank before the engine fires.
- Intermittent no-start condition.
- Stalling, especially at idle or just after a cold start.
- Rough running, hesitation or stumble under load on Bank 2.
- Reduced power and possible limp mode.
- Reduced fuel economy from the default timing strategy.
3Common Causes of the P0393 Code
- Disconnected, loose or corroded CMP-B (Bank 2) connector.
- Open or shorted-to-voltage signal wiring (often oil-soaked or chafed).
- A failed camshaft position sensor “B”.
- Poor or broken ground causing the circuit to default high.
- Oil leaking into the connector from a valve cover or cam seal.
- Damaged reluctor / tone ring on the exhaust camshaft.
- ECM signal-conditioning fault (rare — verify wiring and sensor first).
4How Serious Is P0393? Can You Keep Driving?
Don't leave P0393 too long. The engine can run on a default timing value, but a high or open CMP-B circuit commonly causes long cranks, hard starts, stalling and sometimes a no-start. Short distances are usually fine, but diagnose it promptly so a stall or no-start doesn't leave you stranded.
5How to Diagnose the P0393 Code
The job is to confirm whether the ECM is getting a clean cam signal:
- Read codes and freeze-frame with a scan tool such as the iCarsoft CR Max P; note any companion codes.
- View live data: compare engine RPM against camshaft “B” RPM/status while cranking — if engine RPM rises but cam-B stays at zero, the ECM is blind to that sensor.
- Inspect the Bank 2 CMP-B connector and harness for oil, corrosion, bent pins and chafing.
- Back-probe the sensor for reference voltage, ground and signal; check for a short to voltage.
- Wiggle-test the harness while watching live data to catch intermittents.
6Steps to Fix the P0393 Error Code
- Reconnect and clean the CMP-B (Bank 2) connector; apply dielectric grease and make sure it locks fully.
- Repair or replace any chafed, oil-soaked, shorted or open wiring and restore a clean ground.
- Fix the underlying oil leak (e.g. a valve cover gasket) so the connector won't re-contaminate.
- If wiring and ground check good, replace the Bank 2 camshaft position sensor “B” with an OEM-quality part.
- Clear the code and confirm the cam-B signal returns to a normal pulsing pattern in live data.
- Inspect the reluctor / tone ring if the signal is still abnormal after replacement.
- Road-test and confirm P0393 and the long-crank/stall symptoms are gone.
7Why the Cam Signal Matters
The camshaft position sensor tells the ECM exactly where the valves are so it can time fuel injection and spark to each cylinder. When the Bank 2 cam signal drops out, the ECM has to guess with a default strategy — which is why starting drags, idle gets rough and power falls off. A clean connector, intact wiring and a healthy sensor are what keep that timing reference honest.
8Which iCarsoft Tool to Use
The iCarsoft CR Max P is well suited to a P0393. Beyond reading and clearing codes across all systems, its live data lets you watch the camshaft “B” signal against engine RPM while cranking — so you can tell a true sensor dropout from a wiring or connector fault before buying parts.
With CAN-FD support and coverage for 58 vehicle makes, it also confirms the cam signal reads correctly again after the repair.
Recommended for P0393
iCarsoft CR Max P
Pro bi-directional scan tool with live camshaft/crankshaft signal data, CAN-FD and full-system diagnostics across 58 car brands — to read the cam-B signal and verify a P0393 repair.
$599.99 · was $819.99 · lifelong free updates
Shop CR Max P See full specs9P0393 Repair Cost
Cost depends on whether it's the connector, the wiring or the sensor. Typical ranges (parts + labor):
| Repair | Typical cost |
|---|---|
| Diagnostic (scan) | $75–$150 |
| Camshaft sensor (Bank 2) replacement | $150–$350 |
| Wiring / connector repair | $80–$300 |
| Valve cover gasket (oil contamination) | $150–$400 |
| Reluctor / tone ring repair | $300–$700 |
These are general estimates — get a quote once the specific cause is confirmed.
10Prevention & Regular Maintenance
- Use OEM or known-quality sensors and connectors when replacing.
- Fix oil leaks promptly so they don't soak sensor connectors.
- Keep up with oil changes to protect cam phasers and timing components.
- Inspect harnesses near hot or moving parts for chafing during service.
- Apply dielectric grease and fully seat connectors after any engine work.
11Related Trouble Codes
12P0393 — Frequently Asked Questions
Can I drive with a P0393 code?
Short trips usually, but expect possible long cranks or stalling. Diagnose it promptly to avoid an intermittent no-start.
Does P0393 mean the sensor is bad?
Not necessarily — it's a high-voltage circuit fault. Loose connectors, oil contamination and broken grounds are common non-sensor causes.
What does the “B” mean?
Sensor “B” conventionally refers to the exhaust camshaft sensor; Bank 2 is the side that does not contain cylinder #1.
Could a timing chain cause P0393?
A “circuit high” is usually electrical, but a damaged reluctor/tone ring or timing issue can contribute if the signal stays abnormal after a good sensor and wiring.
How do I reset the P0393 code?
Repair the fault first, then clear the code with a scan tool such as the iCarsoft CR Max P and verify a normal cam signal in live data.
13References
- SAE International, J2012 — Diagnostic Trouble Code Definitions (the standard that defines P0393).
- Wikipedia, Crank / cam position sensor — background on how position sensors time the engine.
