P1C39

Code

Generic P — Powertrain

Turbocharger Boost Pressure Sensor 'A' Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 7 EN: 11 RU: 7

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty boost (MAP/boost) pressure sensor 'A'
Damaged or corroded sensor connector or wiring (open, short to power/ground, high resistance)
Lost or unstable 5V reference or signal ground from ECU
Intake or boost hose leaks, loose clamps, or disconnected/vacuum lines
Sticking or mis-adjusted wastegate/boost control actuator or solenoid
Contaminated or clogged sensor port (oil, soot)

Symptoms

Check Engine MIL illuminated (with P1C39 stored)
Reduced engine power, limp mode or loss of boost control
Erratic or inconsistent boost behavior (surges, overboost, underboost)
Poor drivability, hesitation, or loss of performance
Possible increased smoke or fuel consumption if fueling is affected

What to check

Read and record freeze frame data and live boost/sensor values with a scan tool
Visually inspect boost sensor connector and wiring for damage, corrosion, or loose pins
Check vacuum/boost hoses and intercooler connections for leaks, cracks or loose clamps
Verify 5V reference and ground at the sensor connector with ignition on (no start) using a multimeter
Measure sensor output voltage while slowly applying boost (engine running or calibrated pressure source)
Compare sensor output to expected pressure (scan tool PID or lab pump) and to ambient atmospheric reference

Signal parameters

Supply/reference voltage: typically ~5.0 V (check OEM spec)
Signal output: typically ~0.5–4.5 V across the sensor pressure range (varies by sensor/vehicle)
At atmospheric pressure (near 1 bar abs) expect a mid-range voltage (often ~2.0–2.5 V, vehicle-dependent)
Signal should change smoothly and proportionally as boost pressure rises and falls
No short to battery (near 12 V) or short to ground (near 0 V) on the signal circuit

Diagnostic algorithm

Retrieve freeze frame and live data (boost pressure PID, commanded boost, wastegate duty, MAP sensor voltage). Note conditions when the code set.
Perform a visual inspection: sensor, connector, wiring harness routing, and boost/vacuum hoses. Repair any obvious damage.
With ignition ON (engine off), confirm 5V reference and ground at the sensor connector. No 5V or poor ground suggests wiring/ECU issue.
Start engine and monitor the sensor signal voltage with a scan tool while varying engine load. Signal must respond smoothly to changes in boost.
Using a handheld vacuum/pressure pump on the sensor port (engine off) or controlled boost while running, apply known pressures and verify sensor output follows expected volts/pressure curve. Compare to OEM spec.
If signal is erratic or out of range but wiring and supply are good, swap in a known-good sensor (if available) to confirm sensor vs wiring/ECU.
If sensor and wiring check good, inspect and test boost control components (wastegate, actuator, boost control solenoid) for proper operation and leaks.
Check for intercooler/charge pipe leaks and repair as needed, then clear codes and road-test to confirm repair.
If problem persists with correct sensor, wiring, and control components, consider ECU input circuit diagnosis or replacement per OEM procedure.

Likely causes

Broken/loose wiring or poor connector connection at the boost sensor
Boost sensor contamination or internal failure
Vacuum/boost hose leak between turbo and sensor intake
Faulty boost control solenoid causing abnormal boost and sensor readings

Fault status

⚠️ Status

Turbocharger Boost Pressure Sensor 'A' signal out of range or performing inconsistently. Control module flagged circuit range/performance fault (P1C39).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 3.0 hours