Code
B1220
FIAT
B — Body
Fuel tank pressure sensor short to positive
Views:
UK: 2
EN: 13
RU: 4
AI status
Completed
Completed
100%
Causes
- Damaged or chafed wiring contacting battery/ignition feed
- Corroded, loose or contaminated connector pins
- Short inside the fuel tank pressure sensor
- Water or debris in connector causing voltage feed-through
- Recent aftermarket electrical work or accessories connected to same circuit
- Rare: ECU/PCM internal fault or shorted protection device
Symptoms
- Malfunction Indicator Lamp (MIL) on / fault stored
- Failed/failed EVAP system readiness or emissions test
- Evap system tests cannot run or report incorrect tank pressure
- Possible fuel odor if EVAP venting is affected
- Usually no major drivability loss, but EVAP-related warnings and diagnostic issues
What to check
- Read freeze frame and related codes with a scan tool
- Visually inspect sensor connector and wiring along harness to tank for damage, corrosion, or recent repairs
- Disconnect the sensor connector — see if code clears or changes
- Backprobe signal wire with ignition ON and measure voltage relative to ground
- Check for battery voltage on the signal wire with ignition OFF (indicates short to fused battery circuit)
- Inspect for aftermarket accessories tied into fuel tank/EVAP wiring
Signal parameters
- Expected: sensor uses a 5V reference; output typically within ~0.5–4.5 V proportional to tank pressure
- At atmospheric (no vacuum/pressure) output often near mid-scale (~2–3 V) — consult vehicle-specific data for exact values
- Short-to-positive condition: signal wire shows near reference/battery voltage or exceeds normal maximum (>4.5 V)
- Sensor supply/reference (with key ON): ~5 V; sensor ground: near 0 V
Diagnostic algorithm
- Retrieve full DTC list and freeze frame data from the vehicle scan tool and note conditions when fault set.
- Perform visual inspection of harness and connector at the fuel tank pressure sensor for damage, corrosion, bent pins, or signs of water intrusion.
- With ignition OFF, disconnect the sensor. Check continuity from the signal pin to chassis ground and to battery positive to identify unintended shorts (continuity to battery indicates short to positive).
- With ignition ON (engine off), backprobe the sensor connector signal wire and measure voltage relative to good chassis ground. Compare to expected value from signal_params. If signal equals battery voltage or reference voltage out of range, note reading.
- Turn ignition OFF and measure resistance between the signal wire and the vehicle battery positive. A low resistance indicates a short to positive. Do the same between signal wire and sensor body/ground to rule out internal short to ground.
- If wiring checks show open/short in harness, repair or replace damaged section. If wiring appears good, reconnect sensor and measure sensor output while applying known pressures using a hand vacuum/pressure pump to verify sensor linearity and range.
- If sensor reads out-of-range or is non-linear while wiring is confirmed good, replace the fuel tank pressure sensor.
- After repairs, clear codes, cycle ignition and perform drive/EVAP system test and confirm code does not return. Recheck readiness monitors if required for emission testing.
- If all wiring and sensor are good but problem persists, consider ECU/PCM input circuit fault and consult factory documentation before replacement.
Likely causes
- Damaged insulation on sensor harness where it rubs chassis and contacts a fused 12V supply
- Connector pushed onto a power terminal or contaminated with conductive debris
- Sensor internal electronic failure allowing supply to appear on signal line
- Incorrect or reversed connector after service or replacement
Fault status
Status
Fuel tank pressure sensor circuit shorted to positive voltage detected; PCM/ECU has stored B1220 and disabled normal evap pressure readings.
Repair difficulty: Medium
Diagnostic time: 1-2 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email