P1201

Code

CHRYSLER P — Powertrain

(Alternative Fuel) Gas Mass Sensor Circuit Range/Performance

Brand: CHRYSLER

Type: P — Powertrain

Views: UK: 36 EN: 56 RU: 41

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Page language: EN

Causes

Failed or degraded gas mass (fuel) sensor
Open, shorted or damaged wiring harness to sensor
Corroded, loose or contaminated sensor connector
Missing or incorrect reference voltage or poor ground
Clogged fuel/gas filter or regulator affecting flow
Contaminated sensor element (oil, deposits)

Symptoms

Check Engine Light (MIL) illuminated
Poor drivability: hesitation, stumble, rough idle or stalls
Hard starting on alternative fuel or inability to run on gas fuel
Degraded fuel economy
Surging or inconsistent engine response under load
Possible increased emissions or failed emissions test

What to check

Retrieve freeze frame and live data with a scan tool; note fuel type and operating conditions when fault set
Visually inspect sensor, connector and wiring for damage, corrosion or contamination
Wiggle test wiring and connector while monitoring live PID for intermittent changes
Check for related stored codes (fuel pressure, regulator, ECU communication)
Verify proper fuel filter condition and regulator operation
Confirm proper fuel composition and system transfer (if vehicle switches between fuels)

Signal parameters

Sensor reference voltage should be present (typically referenced to vehicle 5 V supply) — verify with multimeter
Sensor ground should be near 0 V with good continuity to chassis/ECU ground
Sensor output will vary with gas flow/engine load — output should change smoothly with throttle
Expected output range is within the ECU’s analog input limits (0–5 V); output stuck at 0 V, near reference, or erratic indicates fault
No excessive noise or voltage spikes on the signal line during operation

Diagnostic algorithm

Read and record freeze frame data and all stored codes. Clear codes and perform a drive cycle to reproduce the fault.
Perform a careful visual inspection of the gas mass sensor, connector and wiring harness. Look for damage, corrosion, or evidence of gas/oil contamination.
With connector disconnected, inspect pins for corrosion, bent pins or contamination. Repair or replace connector as needed.
Backprobe the sensor harness with a multimeter/oscilloscope: verify reference voltage, ground continuity, and sensor output voltage while varying engine load. Compare behavior to expected (smooth, proportional change).
Perform a wiggle/strain test on wiring while monitoring live data to identify intermittent opens/shorts.
Check fuel gas filter and regulator for restriction or failure that could cause abnormal flow readings; replace filter if clogged and verify regulator pressure/operation per factory procedure.
If wiring and supply are good but output is implausible, substitute a known-good sensor or bench-test the suspect sensor (if service information permits).
If sensor and wiring check good, inspect ECU input circuit and related fuses; consult manufacturer service information for ECU tests and software/PCM updates.
After repairs, clear codes and repeat drive cycle; verify code does not return and vehicle drivability is restored.

Likely causes

Sensor element failure or internal drift
Damaged wiring (pinched, chafed) between sensor and ECU
Poor connector contact (corrosion/loose pin)
Loss of sensor 5V reference or ground
Restricted gas supply (clogged filter/regulator) causing abnormal sensor reading

Fault status

⚠️ Status

Alternative fuel gas mass sensor circuit - signal out of range or poor performance; manufacturer-specific fault recorded.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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P1201 — (Alternative Fuel) Gas Mass Sensor Circuit Range/Performance