Code
P1873
MITSUBISHI
P — Powertrain
Gearbox potentio.#1 error(SIG.2)
Views:
UK: 6
EN: 7
RU: 6
AI status
Completed
Completed
100%
Causes
- Faulty gearbox/shift position potentiometer (sensor)
- Open or short in potentiometer signal wiring
- Corroded, loose, or damaged connector/terminal at sensor or TCM
- Water ingress or contamination of sensor connector
- Poor ground or missing 5 V reference from TCM
- Intermittent wiring fault due to chafing or broken wire
Symptoms
- Transmission enters limp/reduced-shift mode
- Incorrect gear indicator or no gear selection displayed
- Inability to shift or harsh/unexpected shifts
- Transmission warning lamp or check engine light illuminated
- Vehicle may refuse to move or stays in a single gear
What to check
- Scan for additional codes and note freeze frame / live data
- Visual inspection of gearbox potentiometer connector and wiring for damage, corrosion, or water
- Check that connector is fully seated and locking tab engaged
- Measure reference voltage and ground at the potentiometer connector (key ON, engine OFF)
- Probe potentiometer signal voltage while moving gear selector through positions (observe change)
- Wiggle test wiring while monitoring signal for intermittent changes
Signal parameters
- Typical connector: 3 wires — 5 V reference, signal, ground (verify in vehicle service manual)
- Reference voltage: approx. 4.8–5.0 V (key ON)
- Signal voltage: varies with selector position, typically ~0.5 V to ~4.5 V across positions
- Open circuit: signal may float or read near 0 V or battery voltage depending on circuit
- Short to ground: signal near 0 V; short to 5 V: signal near 5 V
- Resistance across potentiometer element will change smoothly with selector position (consult service manual for exact ohms)
Diagnostic algorithm
- Retrieve full list of DTCs and note conditions (gear, temperature, battery voltage). Clear codes and see if P1873 returns.
- Perform visual inspection of wiring and connector at gearbox potentiometer; repair damaged wires or terminals before electrical testing.
- With ignition ON (engine OFF), backprobe the potentiometer connector: verify 5 V reference present and good ground. If 5 V absent, trace supply back to TCM / fuse.
- Monitor potentiometer signal voltage while moving gear selector through all positions; signal should change smoothly without jumps. Record values.
- If signal is stuck, open, or erratic, disconnect sensor and check resistance of potentiometer element across terminals while moving selector. Compare to manufacturer spec.
- Perform wiggle test on harness and connector while monitoring signal to locate intermittent shorts/opens. Repair any chafing or broken wires and protect wiring.
- Check continuity and resistance of wiring between potentiometer and TCM; repair any high resistance or opens.
- If wiring and connector are good but sensor out of spec, replace gearbox potentiometer and retest.
- After repairs, clear codes, perform relearn or calibration procedures if required by manufacturer, then test drive to confirm code does not return.
- If problem persists after sensor/wiring replacement, consider TCM input circuit fault and perform TCM bench testing or replacement as last resort.
Likely causes
- Damaged connector or corroded terminals at gearbox potentiometer
- Broken or shorted signal wire between potentiometer and TCM
- Worn or failed potentiometer inside gearbox
- Missing or low 5 V reference or poor ground
- Intermittent fault due to moisture/contamination
Fault status
Status
Gearbox potentiometer #1 signal (SIG.2) fault detected — signal out of range, open, short, or intermittent. Inspect sensor, wiring, and connector; verify 5 V reference and ground.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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