P1398

What Does Code P1398 Mean?

DTC P1398 indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a “High Input” condition in the electrical circuit for Variable Valve Timing (VVT) Solenoid “B”. This typically signifies that the voltage signal on the control circuit for VVT Solenoid B is continuously or intermittently exceeding the expected operational threshold, often registering near battery voltage (B+) when the ECM expects a lower voltage or a specific pulse-width modulated (PWM) signal. The VVT system is crucial for optimizing valve overlap, timing, and lift, which directly influences engine performance, fuel efficiency, and emissions across various RPMs and load conditions. Solenoid “B” usually refers to a specific camshaft position actuator, which varies depending on the vehicle manufacturer and engine configuration (e.g., exhaust camshaft on an inline engine, or a particular bank/intake/exhaust camshaft on a V-engine). When a high input is detected, it suggests an open circuit, a short to voltage, or a fault within the solenoid’s internal windings, preventing the ECM from effectively controlling the camshaft position actuator.

Common Symptoms

• Illuminated Malfunction Indicator Lamp (MIL) on the dashboard.
• Rough idle or unstable engine idle speed.
• Reduced engine performance, particularly noticeable during acceleration or at higher RPMs.
• Increased fuel consumption due to inefficient valve timing.
• Engine hesitation, stumbling, or a general lack of power.
• Potential failure during emissions testing.

What Causes the Code P1398?

• Faulty VVT Solenoid “B”: Internal electrical failure within the solenoid itself, such as an open circuit in the solenoid’s coil windings, leading to an abnormally high resistance or infinite resistance (open).
• Wiring Harness Issues: An open circuit, short to battery voltage (B+), or excessively high resistance in the wiring harness connecting the VVT Solenoid “B” to the ECM/PCM. This includes damaged insulation, broken wires, corroded terminals, or loose connections at the solenoid or ECM connector.
• Contaminated Engine Oil: While primarily an electrical circuit code, severely contaminated or incorrect viscosity engine oil can impede solenoid plunger movement, potentially causing the solenoid to draw an incorrect current or exhibit erratic electrical characteristics that trigger the high input. However, this is less common for a “circuit high” code compared to a mechanical VVT code.
• Faulty Engine Control Module (ECM/PCM): Although less common, an internal malfunction within the ECM/PCM, specifically a faulty VVT driver circuit or internal pull-up resistor, could erroneously report a high input condition on the solenoid’s control circuit.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is essential to accurately pinpoint the root cause of P1398:

1. Retrieve and Analyze Freeze Frame Data: Connect an OBD-II scanner and record all stored DTCs and associated freeze frame data. This data provides crucial information about engine operating conditions (RPM, engine load, coolant temperature, etc.) when the P1398 code was set. This context can help recreate the fault.
2. Visual Inspection:
   • Locate VVT Solenoid “B”. Consult the vehicle-specific service manual for exact location and designation.
   • Inspect the electrical connector for VVT Solenoid “B” for signs of corrosion, bent pins, oil contamination, or damage.
   • Examine the wiring harness leading to the solenoid for any chafing, cuts, signs of rodent damage, or evidence of shorting to ground or B+.
   • Verify engine oil level and condition. While not a direct electrical cause, extremely low or severely contaminated oil can sometimes indirectly affect VVT solenoid operation or lead to premature failure.
3. Electrical Circuit Tests (Key On, Engine Off – KOEO):
   • Disconnect the electrical connector from VVT Solenoid “B”.
   • Using a Digital Multimeter (DMM), identify the power supply wire (usually 12V) and the control wire from the ECM.
   • Power Supply Test: With the ignition ON, measure voltage on the power supply wire relative to chassis ground. Expect to see battery voltage (B+). If no voltage, trace the circuit back to the fuse box or relay.
   • Continuity Test (ECM Control Wire): Turn ignition OFF. With the ECM connector disconnected (follow service manual procedures for safe ECM disconnection), perform a continuity test between the control wire terminal at the VVT solenoid connector and its corresponding terminal at the ECM connector. Resistance should be less than 5 ohms. An open circuit (OL) indicates a break in the wire.
   • Short to Ground/Voltage Test: Check both power and control wires for shorts to ground and shorts to B+. Place the DMM positive lead on each wire terminal and the negative lead on a known good chassis ground (for short to ground) or B+ (for short to voltage). Readings should be OL.
4. VVT Solenoid “B” Resistance Test:
   • With the VVT Solenoid “B” still disconnected from the wiring harness, use a DMM to measure the internal resistance across the solenoid’s two terminals.
   • Compare the measured resistance to the manufacturer’s specifications (typically found in the service manual, often ranging from 6 to 15 ohms). An “OL” (open loop) reading indicates an internal open circuit within the solenoid, confirming a faulty solenoid. Readings significantly outside the specified range also indicate a fault.
5. ECM/PCM Output Signal Test (Advanced): If the solenoid and wiring test good, and the code persists, an oscilloscope may be used to observe the PWM control signal from the ECM on the control wire while the engine is running and VVT conditions are met. This will verify if the ECM is sending the correct signal. If the signal is consistently high (near B+) when it should be pulsed or low, and the wiring is good, it points to a potential ECM fault.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace VVT Solenoid “B”: If the VVT solenoid fails the resistance test, exhibits an open circuit, or is confirmed to be faulty during a functional test, replace it with a new, OEM-quality part. Ensure the mounting surface is clean and the new solenoid is properly seated and torqued.
• Repair or Replace Wiring Harness Components: If the diagnostic steps reveal an open circuit, short to voltage, or high resistance in the wiring harness or connectors, perform precise repairs. This may involve splicing in new sections of wire, replacing corroded or damaged connectors, or addressing loose terminals. Always use appropriate crimping tools and heat-shrink tubing for durable repairs.
• Engine Oil Service: If the engine oil was found to be severely contaminated or at an incorrect level, perform an immediate oil and filter change with the manufacturer-specified oil viscosity. While not a primary fix for an electrical circuit code, maintaining proper oil condition is critical for overall VVT system health.
• ECM/PCM Replacement or Reprogramming: If all other components (solenoid, wiring) are verified to be in perfect working order, and the ECM consistently fails to output the correct control signal for VVT Solenoid “B”, the ECM/PCM may be faulty. This is a rare occurrence and should only be pursued after exhausting all other diagnostic possibilities. ECM replacement often requires reprogramming by a qualified technician using specialized tools.

Mechanics’ Tips: Always confirm the specific designation of “Solenoid B” for the vehicle being worked on, as it varies significantly between manufacturers and engine configurations. After any repair, clear the DTCs from the ECM and perform a comprehensive test drive under varying engine loads and RPMs to ensure the fault does not return and the VVT system functions correctly. Some vehicles may require an adaptive learning procedure after VVT component replacement, so consult the factory service manual.