P27F1

Code

Generic P — Powertrain

Transmission Range Control B Position Sensor/Switch Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 19 EN: 26 RU: 23

AI status

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Page language: EN

Causes

Short to ground on the TRC B signal wire
Open or corroded connector or wiring (high resistance)
Faulty transmission range/park position sensor (B element)
No reference voltage or poor ground to the sensor
PCM input circuit fault (rare)
Corroded/loose battery/vehicle ground affecting sensor reading

Symptoms

MIL/Check Engine light illuminated
Transmission may not engage correct gear or may default to limp/limited mode
Incorrect gear indicator on dash or no gear displayed
Intermittent shifting problems or inability to start in selected gear (safety interlock)
Stored transmission-related trouble codes

What to check

Read and record freeze frame and related transmission/gear codes
Visually inspect harness and connector at transmission range sensor for damage, corrosion, bent pins, or water intrusion
Check battery voltage and main grounds to ensure proper supply
Backprobe and measure TRC B signal voltage with ignition ON (engine off) and while moving shifter through positions
Check for reference 5V supply and a good ground at the sensor connector
Perform wiggle test on wiring while monitoring signal for intermittent changes

Signal parameters

Reference voltage to sensor: nominally 5V (±0.25V) with ignition ON
Expected TRC B signal range: ~0 to 5V depending on gear (specific values vary by design)
Circuit Low condition: signal at or near 0V (typically
Expected resistance: open circuit when disconnected between signal pin and ground should be >10 kΩ; short to ground will show near 0 Ω
Sensor ground should be near chassis ground (low milliohm continuity)

Diagnostic algorithm

Confirm the code, note freeze frame data, and check for other related codes (TRC A/C, transmission control codes).
Visually inspect the sensor connector and wiring harness at the transmission for damage, corrosion, or pin push-out. Repair obvious damage.
With ignition ON (engine off), backprobe the sensor connector: verify reference (~5V), sensor signal, and ground presence. If reference or ground missing, trace power/ground circuits.
If reference and ground are good but signal is low (
If no short to ground is found, check sensor resistance/outputs per service data (or compare signals from sensors A/C if available). Replace sensor if it fails output checks.
Perform a wiggle test on harness while monitoring live signal for intermittent faults; repair chafed wires or reterminate connector as needed.
After repair or replacement, clear codes and perform a road test while monitoring transmission range sensor signals and shift behavior to confirm repair.
If wiring and sensor check good, consider PCM input fault—verify with manufacturer procedures before replacing PCM.

Likely causes

Damaged or chafed signal wire shorted to ground
Corroded/loose connector at the transmission range sensor
Failed transmission range (gear position) sensor B
Missing or low reference 5V supply or bad sensor ground

Fault status

⚠️ Status

Transmission Range Control B position sensor/switch circuit voltage low (signal below expected level). Possible short to ground, open/low sensor output, or wiring/connector fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours