P1350

What Does Code P1350 Mean?

DTC P1350 stands for Fuel Level Sensor B Intermittent/Bypass Line Monitor. This code indicates that the Powertrain Control Module (PCM), also referred to as the Engine Control Module (ECM), has detected an intermittent or inconsistent electrical signal from the Fuel Level Sensor ‘B’ circuit, or an issue with the bypass line monitoring system, which often integrates with fuel level and evaporative emissions (EVAP) system diagnostics. In many vehicle applications, particularly Ford models, “Fuel Level Sensor B” does not refer to a direct fuel gauge sender but rather to a component like the Fuel Tank Pressure (FTP) sensor. The FTP sensor monitors pressure within the fuel tank, a critical input for the EVAP system’s leak detection and purge operations. An intermittent signal from this sensor, or a malfunction in the associated bypass line monitoring circuit, can lead the PCM to conclude that its ability to accurately assess fuel tank conditions, including changes in fuel level or vapor pressure, is compromised. The “Bypass Line Monitor” aspect often pertains to the PCM’s diagnostic routine for the EVAP system, where a specific bypass line or solenoid circuit is monitored to ensure proper system function during various self-tests. The PCM detects this problem when the sensor’s voltage output or the monitored bypass circuit’s integrity falls outside predetermined operating parameters or fluctuates erratically, suggesting a temporary loss of signal, a short, an open circuit, or an internal sensor fault that prevents consistent data reporting.

Common Symptoms

• Check Engine Light (CEL) illumination: This is the most common and often the only immediately noticeable symptom.
• Erratic or inaccurate fuel gauge readings: The fuel gauge may jump, stick, or display incorrect fuel levels if the code is directly impacting a secondary fuel level sensor.
• Difficulty passing emissions testing: A malfunctioning EVAP system, often indicated by issues with the FTP sensor or bypass monitoring, will prevent readiness monitors from completing, leading to emissions test failure.
• Reduced fuel economy: While not a direct symptom, an impaired EVAP system can sometimes indirectly affect fuel trim, though this is less common for an intermittent sensor signal.
• Other EVAP-related codes: P1350 may be accompanied by other EVAP system diagnostic trouble codes.

What Causes the Code P1350?

• Faulty Fuel Tank Pressure (FTP) Sensor: This is a very common culprit, especially if the sensor’s internal components become intermittently faulty.
• Damaged, corroded, or loose wiring harness: The wiring leading to the FTP sensor or the specific bypass line monitoring components can become chafed, cut, or experience terminal corrosion, leading to intermittent signal loss.
• Poor electrical connections: Connectors at the FTP sensor, EVAP system components, or the PCM can suffer from oxidation, bent pins, or insufficient tension, causing intermittent contact.
• Malfunctioning EVAP bypass solenoid/valve: If the “Bypass Line Monitor” refers to a specific solenoid or valve that directs vapor flow, a fault within this component or its circuit can trigger P1350.
• Vacuum leaks or blockages in EVAP lines: While less direct for “intermittent sensor,” a leak or blockage in the bypass line or related EVAP hoses could cause erratic pressure readings for the FTP sensor.
• PCM internal fault: Although rare, an internal malfunction within the Powertrain Control Module could intermittently misinterpret sensor data or fail to properly monitor the bypass line.

How to Diagnose and Troubleshoot

Diagnosing P1350 requires methodical electrical and visual inspection, often involving an OBD-II scanner and a digital multimeter (DMM).

1. Retrieve and Analyze Freeze Frame Data: Connect an OBD-II scanner to confirm P1350 and retrieve any stored freeze frame data. This data provides a snapshot of vehicle conditions (engine RPM, temperature, vehicle speed, etc.) when the code was set, which can offer clues to the intermittent nature of the fault. Note any other pending or stored DTCs that might be related.
2. Visual Inspection of EVAP System Components and Wiring: Locate the FTP sensor (typically mounted on or near the fuel tank) and inspect its wiring harness and connector for any signs of damage, fraying, corrosion, or loose connections. Trace the wiring back towards the PCM as far as possible, checking for chafing where it passes through body panels or near exhaust components. Inspect all associated EVAP lines, including the bypass line if identifiable, for cracks, disconnections, or blockages.
3. Electrical Circuit Test at the FTP Sensor (or relevant ‘B’ sensor):
   • With the ignition ON and engine OFF, disconnect the FTP sensor connector.
   • Using a DMM, check for proper reference voltage (typically 5V) at one of the harness terminals.
   • Check for a good ground signal at another terminal.
   • Inspect the signal return wire for continuity back to the PCM. A high resistance or open circuit indicates a wiring fault.
   • Reconnect the sensor. With the scanner, monitor the FTP sensor’s live data PIDs (Parameter Identifiers). Observe the voltage or pressure readings. Wiggle the wiring harness near the sensor and along its path to the PCM to see if the readings fluctuate erratically, indicating an intermittent connection.
4. FTP Sensor Output Test: If the wiring appears intact, the issue may lie within the sensor itself.
   • Monitor the FTP sensor’s live data while the vehicle is idling and then with the engine off after driving. The pressure should stabilize after shutdown.
   • If available, use a vacuum/pressure pump to apply a small, controlled amount of pressure (e.g., 1-2 inches H2O) and vacuum to the FTP sensor’s port while monitoring its output voltage/pressure. The readings should change smoothly and predictably without intermittent drops or spikes.
5. EVAP Bypass Line/Solenoid Monitoring (if applicable): If the “Bypass Line Monitor” points to a specific solenoid or valve (e.g., EVAP bypass solenoid), verify its circuit integrity.
   • Check for power and ground at the solenoid connector.
   • Measure the resistance of the solenoid’s coil. Compare to manufacturer specifications. An open circuit or widely varying resistance suggests a faulty solenoid.
   • If bi-directional controls are available on the scanner, attempt to actuate the solenoid and listen/feel for its operation while monitoring relevant PIDs.
6. PCM Pin-out Check: If all component and wiring checks are inconclusive, perform continuity and voltage checks directly at the PCM connector pins corresponding to the FTP sensor or bypass line circuit. This isolates whether the fault lies in the harness or potentially within the PCM itself.

Recommended Repairs and Solutions

Once the root cause of P1350 has been pinpointed through thorough diagnosis, the following repairs are typically recommended:

• Repair or Replace Damaged Wiring Harness: If visual inspection or electrical tests reveal chafed, corroded, or open/shorted wires, carefully repair the affected sections using appropriate automotive-grade wiring and connectors. Ensure proper weather sealing for any splices.
• Replace the Fuel Tank Pressure (FTP) Sensor: If the FTP sensor is determined to be faulty, replace it with a new, high-quality OEM or equivalent aftermarket part. Be aware that accessing the FTP sensor often requires lowering or removing the fuel tank in some vehicles, which can be a time-consuming procedure. Always relieve fuel system pressure and follow all safety precautions when working near fuel systems.
• Replace Malfunctioning EVAP Bypass Solenoid/Valve: If diagnostic tests confirm a fault in an EVAP bypass solenoid or valve (e.g., open circuit, stuck valve), replace the component. Verify its proper function after installation.
• Clean or Repair Electrical Connectors: If corrosion or poor contact at connectors is identified, clean the terminals thoroughly using electrical contact cleaner and a small brush. If terminals are severely damaged or bent, replace the connector shell and terminals as needed. Apply dielectric grease to protect against future corrosion.
• Address EVAP System Leaks/Blockages: If a leak in an EVAP line or a blockage (e.g., in the bypass line) is found, repair or replace the affected hose or component. Ensure all EVAP system lines are securely connected and free from damage.
• PCM Replacement/Reprogramming: Only consider PCM replacement or reprogramming as a last resort, after all other potential causes have been thoroughly investigated and ruled out. This is a rare cause for P1350.

Mechanics’ Tips: Always clear the DTCs after performing any repairs. Conduct multiple drive cycles under varying conditions to ensure that the repair has resolved the issue and that all EVAP readiness monitors have completed successfully. For Ford vehicles, consult relevant Technical Service Bulletins (TSBs) as P1350 can sometimes be addressed by specific software updates or revised procedures related to the EVAP system. When working on fuel systems, always prioritize safety by disconnecting the battery, wearing appropriate personal protective equipment, and ensuring good ventilation.