P27EF

Code

Generic P — Powertrain

Transmission Range Control B Position Sensor/Switch Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 28 RU: 18

AI status

Completed

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Page language: EN

Causes

Open circuit in the B position sensor/switch wiring
Corroded, loose or damaged connector at the sensor or PCM
Failed transmission range (PRNDL) sensor or internal switch
Damaged or chafed harness (broken conductor)
Poor ground or power supply to the sensor circuit
Shift linkage misalignment preventing correct switch actuation

Symptoms

Malfunction Indicator Lamp (MIL) or transmission warning lamp on
Gear indicator incorrect or not matching actual lever position
Transmission may not shift or may be stuck in limp/limited mode
Engine may not crank or starter disabled in some gear positions
Intermittent loss of gear selection detection

What to check

Read and record freeze-frame and live data for transmission range sensor values with a scan tool
Visually inspect connector and wiring at the transmission range sensor and PCM
Backprobe the sensor connector to check reference, signal and ground voltages with ignition ON (engine off)
Check continuity and resistance of the signal wire between sensor connector and PCM connector
Wiggle harness and shift linkage while monitoring live data to reproduce the fault
Inspect shift lever/cable for proper adjustment and binding

Signal parameters

Typical reference voltage: about 5 V (depends on vehicle). Signal should change when lever moved into B position
Open-circuit: OL/very high resistance or no signal voltage on the signal pin
Closed/actuated switch: low resistance (near 0 Ω) between switch pin and ground or expected signal reference depending on sensor type
Expected continuity: measurable continuity between sensor signal and PCM signal pin; infinite/open when circuit broken

Diagnostic algorithm

Connect a scan tool, verify P27EF is current or stored, and note related transmission range data and freeze-frame.
Visually inspect the B-position sensor connector and wiring for corrosion, damage, pin push-out or water intrusion. Repair any obvious damage.
With ignition ON (engine OFF), backprobe the sensor connector: verify reference voltage and ground are present. If reference/ground missing, trace to fuse/relay/PCM.
Measure the signal voltage while moving the shifter to the B position. If voltage never changes or is absent, suspect open circuit or bad sensor.
Check continuity of the signal wire from the sensor connector to the PCM connector. Repair any open or high-resistance segments.
If continuity is good, measure sensor resistance (if applicable) or perform bench test per service manual. Replace sensor if out of spec.
If wiring and sensor test good, check PCM connector for bent pins and re-test. Consider PCM bench test or replacement only after exhausting wiring and sensor checks.
After repairs, clear codes, verify proper operation with live data, and perform road test to confirm the fault does not return.

Likely causes

Wiring broken at flex point near transmission or bellhousing
Connector terminals pushed out, corroded, or contaminated
Sensor internal contacts worn or failed
Previous service damage to harness (heat, abrasion)
Water intrusion into connector causing open circuit

Fault status

⚠️ Status

P27EF — Transmission Range Control B Position Sensor/Switch Circuit/Open: PCM detected an open or missing signal on the B-position range sensor/switch circuit. Check wiring and sensor for open circuit or poor connection.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours