What Is OBD Code P1397?
P1397 is a BMW-specific diagnostic trouble code that signals a malfunction in the Camshaft Position Sensor B circuit on Bank 1 (the side of the engine containing cylinder #1). This code is proprietary to BMW vehicles and indicates that the engine control module (DME) has detected an electrical or functional problem with the secondary camshaft position sensor or its wiring circuit.
Unlike standard OBD-II codes, P1397 is part of BMW’s extended diagnostic system and won’t appear on all vehicles. If your BMW is displaying this code, it means the DME has lost proper communication or signal integrity with the camshaft sensor on the intake or exhaust cam on Bank 1.
What Does P1397 Mean?
The Camshaft Position Sensor B monitors the rotational position of the secondary camshaft (typically the exhaust cam or the second intake cam on dual-cam engines). The DME uses this signal to:
- Optimize fuel injection timing
- Control variable valve timing (VVT) systems
- Manage emission control systems
- Ensure proper engine synchronization
When P1397 is triggered, the circuit has failed one or more of the following checks:
- Signal voltage is out of range
- Signal is missing or intermittent
- Wiring continuity is broken
- Sensor resistance is abnormal
- DME communication with the sensor has been lost
Common Symptoms
- Check Engine Light (MIL): The primary indicator; may be steady or flashing
- Rough Idle: Engine may run unevenly at stops or in park
- Reduced Power/Limp Mode: Engine may enter a reduced-power state to protect itself
- Poor Fuel Economy: Inefficient combustion due to incorrect valve timing
- Difficulty Starting: Cold starts may be sluggish or require multiple attempts
- Engine Hesitation: Stumbling or hesitation during acceleration
- Rattling Noise: Valve timing issues can cause a rattling sound from the engine bay
- Stalling: In severe cases, the engine may stall while driving or idling
Possible Causes (Ranked by Frequency)
1. Dirty or Faulty Camshaft Position Sensor
The most common cause of P1397. Camshaft sensors can accumulate carbon deposits, oil sludge, or debris over time, degrading their ability to generate a clean signal. BMW engines are particularly susceptible to carbon buildup on sensors due to direct fuel injection.
2. Wiring Harness Issues
Corroded, pinched, or damaged wiring between the sensor and the DME can interrupt the signal. This is especially common in older BMWs or vehicles exposed to salt and moisture.
3. Loose or Corroded Connector
The sensor connector may be loose, corroded, or improperly seated, causing intermittent signal loss. Water intrusion into connectors is a frequent culprit in BMWs.
4. Failing Camshaft Position Sensor
The sensor itself may be reaching end-of-life. Sensors typically last 80,000–150,000 miles before electrical degradation occurs.
5. Engine Control Module (DME) Malfunction
In rare cases, the DME itself may have a fault in the circuit that reads the camshaft sensor signal. This is less common but possible after water damage or electrical surges.
6. Variable Valve Timing (VVT) System Issues
Problems with the VVT solenoid or timing chain can cause the camshaft to be out of sync, triggering the code even if the sensor is functional.
7. Timing Chain Stretch or Wear
A stretched or worn timing chain can cause the camshaft to drift out of sync with the crankshaft, confusing the sensor signal.
Diagnostic Steps
Step 1: Confirm the Code with a BMW Diagnostic Scanner
Use a BMW-specific diagnostic tool (such as a JTAG, INPA, or professional BMW scanner) to confirm P1397 and check for any related codes. Standard OBD-II scanners may not display this proprietary code clearly. Note the freeze frame data (engine load, RPM, temperature) when the fault occurred.
Step 2: Visual Inspection
Locate the Camshaft Position Sensor B on Bank 1. On most BMWs, this is on the cylinder head near the camshaft. Inspect for:
- Visible damage or cracks on the sensor body
- Oil leaks or excessive sludge around the sensor
- Corroded or wet connector
- Damaged wiring or pinched harness
Step 3: Check Connector and Wiring
Disconnect the sensor connector and inspect for corrosion, water, or loose pins. Clean with electrical contact cleaner if needed. Check the wiring harness for continuity using a multimeter. Resistance should typically be under 1 ohm for a good connection.
Step 4: Test Sensor Resistance
With the connector disconnected, measure the sensor’s resistance with a multimeter. Most BMW camshaft sensors should read between 200–900 ohms (consult your specific model’s service manual for exact specs). Out-of-range readings indicate a faulty sensor.
Step 5: Check Sensor Signal Voltage
With the engine running, use an oscilloscope or advanced multimeter to monitor the sensor signal voltage. The signal should be a clean AC or digital waveform. A flat or erratic signal indicates a failing sensor or wiring issue.
Step 6: Inspect the Timing Chain and VVT System
If the sensor tests good, have a mechanic inspect the timing chain for stretch and the VVT solenoid for proper operation. A stretched chain or stuck solenoid can cause the camshaft to be out of sync.
Step 7: Clear the Code and Test Drive
After repairs, clear the code using your BMW scanner and perform a test drive under various conditions (idle, acceleration, highway speeds). Monitor for code return.
Repair Cost Estimates
Camshaft Position Sensor Replacement
- Parts Cost: $80–$250 (depending on BMW model year and generation)
- Labor Cost: $150–$400 (1–3 hours, depending on engine layout and accessibility)
- Total: $230–$650
Wiring Harness Repair/Replacement
- Parts Cost: $50–$200
- Labor Cost: $100–$300
- Total: $150–$500
Connector Cleaning/Replacement
- Parts Cost: $20–$100
- Labor Cost: $50–$150
- Total: $70–$250
DME Reprogramming or Replacement (Rare)
- Parts Cost: $500–$1,500
- Labor Cost: $200–$500
- Total: $700–$2,000
Timing Chain Inspection/Replacement (If Needed)
- Parts Cost: $300–$800
- Labor Cost: $800–$2,000
- Total: $1,100–$2,800
Note: Most P1397 issues are resolved by sensor replacement or wiring repair, keeping costs in the $200–$650 range. Timing chain work is rarely necessary unless confirmed during inspection.
Can I Still Drive?
Safety Assessment
P1397 is a moderate severity code. While you may be able to drive short distances, it’s not recommended for extended highway driving.
What You Should Know
- Limp Mode: Your BMW may enter reduced-power mode, limiting acceleration and top speed.
- Fuel Economy: Expect significantly worse fuel economy due to incorrect valve timing.
- Engine Damage Risk: Prolonged driving with incorrect valve timing can increase wear on the engine.
- Emissions: The vehicle may fail an emissions test.
- Stalling Risk: In rare cases, the engine may stall unexpectedly.
Recommendation
Have the code diagnosed and repaired within a few days. If you must drive, keep speeds moderate and avoid heavy acceleration. Do not tow or carry heavy loads. If the check engine light is flashing (indicating a misfire), stop driving immediately and have the vehicle towed to a repair facility.
Frequently Asked Questions
Q: Can I drive with P1397?
A: Yes, but not for long distances. Your BMW will likely enter limp mode, reducing power and fuel economy. Driving with this code for extended periods can cause engine damage. Have it diagnosed and repaired within a few days.
Q: Is P1397 the same as a crankshaft sensor code?
A: No. P1397 is specific to the Camshaft Position Sensor B on Bank 1. Crankshaft sensor codes are different (typically P0335 or P0336). However, both sensors work together, and a faulty crankshaft sensor can sometimes trigger camshaft codes indirectly.
Q: Will clearing the code fix the problem?
A: Temporarily, the check engine light may go off, but the underlying issue will remain. The code will return within a few driving cycles. You must address the root cause—whether it’s a dirty sensor, bad wiring, or a failing component.
Q: How much does it cost to fix P1397?
A: Most commonly, $230–$650 for sensor replacement and wiring repair. In rare cases involving DME or timing chain issues, costs can reach $1,500–$2,800. Get a diagnostic scan and quote from a BMW specialist for an accurate estimate.
Q: Can a dirty air filter cause P1397?
A: No. A dirty air filter affects fuel mixture and can trigger different codes (like P0101), but not P1397. P1397 is specific to the camshaft sensor circuit and requires direct inspection of the sensor and wiring.
Q: Is P1397 covered under BMW warranty?
A: If your BMW is still under the factory warranty (typically 3 years/36,000 miles), sensor and wiring issues should be covered. Extended warranties may also cover this. Check your warranty documentation or contact your BMW dealer.