B1220

What Does Code B1220 Mean?

DTC B1220 signifies an detected open circuit within the Fuel Tank Pressure (FTP) sensor’s electrical system. This code is typically manufacturer-specific, predominantly associated with General Motors (GM) vehicles, and relates directly to the Evaporative Emission Control (EVAP) system. The Engine Control Module (ECM), also known as the Powertrain Control Module (PCM), utilizes the FTP sensor to monitor pressure and vacuum levels within the fuel tank. This data is critical for the ECM to perform EVAP system leak detection tests, ensuring that fuel vapors are properly contained and processed rather than released into the atmosphere. When the ECM detects an “open” condition in the FTP sensor circuit, it means there is a complete loss of electrical continuity, preventing a signal from reaching the ECM. This could be due to a broken wire, a faulty sensor exhibiting an internal open, or a poor connection, rendering the EVAP system’s pressure monitoring function inoperative or providing an invalid reading. Consequently, the ECM sets the B1220 code and illuminates the Malfunction Indicator Lamp (MIL).

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be on, indicating a detected fault.
• Inability to Pass Emissions Testing: A non-functional EVAP system due to an open circuit will prevent emission monitors from completing, leading to a failed inspection.
• No Noticeable Drivability Issues: The engine’s performance or fuel economy is typically not affected directly by an open FTP sensor circuit, as it does not directly influence fuel delivery or combustion.
• Potential Difficulty with Fueling: In some rare cases, a completely inoperative EVAP system might subtly interfere with the tank’s venting, leading to premature fuel nozzle shut-off during refueling, although this is more often associated with other EVAP blockages.

What Causes the Code B1220?

• Faulty Fuel Tank Pressure (FTP) Sensor: An internal electrical break within the sensor itself, causing an open circuit.
• Open Circuit in the FTP Sensor Wiring Harness: This includes severed, chafed, corroded, or otherwise damaged wires leading to or from the FTP sensor, preventing current flow. Damage can occur from road debris, abrasion, or rodent activity.
• Corroded or Damaged FTP Sensor Connector: Loose, bent, or corroded pins within the electrical connector at the sensor or harness side can interrupt the circuit continuity.
• Faulty Powertrain Control Module (PCM)/Engine Control Module (ECM): While rare, an internal component failure within the PCM responsible for monitoring the FTP sensor input could manifest as an open circuit detection.

How to Diagnose and Troubleshoot

Diagnosis of B1220 requires a systematic approach using a digital multimeter (DMM) and an OBD-II scanner:

1. Visual Inspection:
   • Begin by visually inspecting the FTP sensor, its electrical connector, and the entire wiring harness leading from the sensor to the PCM. Look for obvious signs of damage, such as frayed or broken wires, melted insulation, corrosion at the connector, or signs of rodent damage. The FTP sensor is typically mounted on the fuel tank or integrated into the fuel pump module.
2. OBD-II Scanner Data Analysis:
   • Connect an OBD-II scanner and check for any other related or pending DTCs.
   • Review freeze frame data associated with B1220 to understand the operating conditions (engine RPM, vehicle speed, engine temperature) when the code was set.
   • If available, monitor the live data stream for the FTP sensor. An open circuit might cause the reading to show a fixed default value (e.g., 0V, -4.9V, or a maximum positive value depending on PCM programming) or an obviously incorrect reading.
3. Digital Multimeter (DMM) Testing (Key Off, Then Key On):
   • Disconnect the FTP Sensor Connector: This isolates the sensor from the harness.
   • Power and Ground Supply Check (Harness Side): With the ignition ON, use the DMM to backprobe the FTP sensor connector (harness side). Verify that the reference voltage (typically 5V for signal, 12V for sensor power on some systems) and a good ground signal are present. Compare readings to vehicle-specific wiring diagrams. An absence of either indicates an open in the power or ground circuit to the sensor.
   • Continuity Check (Harness to PCM): Disconnect both the FTP sensor connector and the PCM connector. Using the DMM in continuity or resistance mode, check for continuity between the signal wire pin at the FTP sensor harness connector and its corresponding pin at the PCM connector. An infinite resistance (open circuit) confirms a break in the signal wire. Perform the same check for the power and ground wires.
   • FTP Sensor Internal Resistance/Continuity Check (Sensor Side): With the sensor disconnected, measure the internal resistance across its terminals according to manufacturer specifications (if available). An internal open circuit in the sensor itself would show infinite resistance where continuity should be present. Note that some FTP sensors are active transducers, not simple resistors, so this test might not be conclusive without specific resistance values or a dedicated sensor test function.
   • Wiggle Test: While monitoring live data with the scanner (if the sensor is showing an intermittent signal) or while performing continuity tests, gently wiggle wiring harnesses and connectors, especially near the sensor and where the harness might be routed through tight areas or susceptible to damage. An intermittent open might be revealed.

Recommended Repairs and Solutions

Once the source of the open circuit has been definitively identified through diagnostic testing, the following repairs are typically performed:

• Repair or Replace Damaged Wiring: If the wiring harness is found to have an open circuit, repair the damaged section. This involves professionally splicing and soldering new wire sections, protected with heat shrink tubing, or replacing the entire segment of the harness if damage is extensive. Ensure proper gauge wire is used.
• Clean or Replace Corroded Connectors: If corrosion or bent pins are found in the FTP sensor connector, carefully clean the pins using electrical contact cleaner and a small brush, or replace the entire connector if damage is severe. Ensure all connections are secure and free of debris.
• Replace the Fuel Tank Pressure (FTP) Sensor: If diagnostic testing confirms the FTP sensor itself is internally open or faulty, replace it with a new, high-quality OEM or equivalent aftermarket unit. This usually requires accessing the fuel tank, often by removing an access panel under the rear seat or by partially dropping the fuel tank, depending on the vehicle model.
• Clear DTCs and Perform Drive Cycle: After any repairs, clear the B1220 DTC and any associated codes using an OBD-II scanner. Then, perform a comprehensive drive cycle to allow the EVAP system monitors to run and verify that the repair has been successful and the code does not return.
• PCM/ECM Replacement (Rare): Only consider PCM/ECM replacement as a last resort, after meticulously ruling out all other potential causes and confirming an internal PCM fault by professional diagnostics. This is a costly repair that often requires reprogramming the new module to the vehicle.