Code
P1143
SUBARU
P — Powertrain
Pressure Sensor Circuit Low Input
Views:
UK: 19
EN: 31
RU: 27
AI status
Completed
Completed
100%
Causes
- Faulty pressure sensor (internal short/open)
- Open or shorted sensor signal wire (short to ground)
- Corroded or loose connector at sensor or PCM
- Failed or weak sensor ground or 5V reference circuit
- Intermittent harness damage (chafing, pinched)
- PCM input fault (rare)
Symptoms
- Check Engine Light (MIL) illuminated
- Reduced engine performance, hesitation or limp-in mode
- Poor fuel economy or rough idle
- Hard starting or stalling in some cases
- Stored diagnostic trouble codes and freeze-frame data
What to check
- Retrieve freeze frame and live data with a scan tool to observe the reported pressure value and related parameters
- Inspect sensor connector and wiring for corrosion, damage, or poor fit
- Backprobe the sensor signal, reference (typically 5 V) and ground with a DVM to verify voltages
- Check continuity and resistance between sensor and PCM pins (with power off) to identify opens or shorts to ground/power
- Compare sensor voltage to known good value or manufacturer specification
- Perform wiggle test of harness while monitoring live data to find intermittent faults
Signal parameters
- Typical sensor reference voltage: ~5.0 V (verify with service manual)
- Expected sensor output range (typical): ~0.5 V (low) to ~4.5 V (high) depending on pressure
- Low-input condition: signal voltage significantly below expected range (near 0–0.5 V)
- PCM input detects signal below threshold for required time and stores code
Diagnostic algorithm
- Connect a scan tool, confirm P1143 and note freeze-frame/live data and any related codes (fuel pressure/MAP/sensor circuits).
- Visually inspect the pressure sensor, connector and wiring for damage, contamination or loose terminals; repair as needed.
- With ignition ON (engine off), backprobe sensor: verify 5V reference present, good ground, and measure signal voltage. If reference or ground is missing, trace to fuse/PCM.
- If reference and ground are good but signal is low, disconnect sensor and measure sensor output with known pressure (or apply known voltage where appropriate) or substitute a known-good sensor.
- Check continuity and insulation between signal wire and chassis ground/power to rule out short circuits; repair wiring harness faults.
- If wiring and sensor test good, inspect PCM connector pins for damage/corrosion; as a last step consider PCM input fault and consult manufacturer procedures before replacement.
- After repairs or replacement, clear codes and perform road test while monitoring live data to verify proper operation.
Likely causes
- Damaged wiring between sensor and PCM causing low signal
- Contaminated or corroded connector reducing signal voltage
- Failed pressure sensor producing low output
- Blown fuse or issue in sensor reference/ground circuit
Fault status
Status
DTC P1143 is stored when the PCM detects the pressure sensor circuit signal voltage is below the expected threshold. The code indicates a low input from the pressure sensor circuit, not necessarily a failed sensor component.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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