P2771: Four Wheel Drive (4WD) Low Switch Circuit

P2771 concerns the input that reports whether the transfer case sits in its low range. GM uses it on 2016 Silverado/Sierra with the MW7 gearbox as a plausibility test in the TCM: if the switch says high range while gear ratio math says low, or the reverse, for at least 0.5 s with fluid between 20 and 130 °C, the Type B code sets. The 2014 LML diesel ECM runs a similar comparison from turbine speed, output speed and ratio. GM's PIP4966B links P2771 on 2007–2011 trucks with Magna transfer cases to a speed-sensor tone wheel shifting on its shaft, or output shaft play, that corrupts the speed signal. Toyota's T-SB-0093-25 shows P2771 with subtype 11 (short to ground) on 2024–2025 Tacoma, fixed with a new shift actuator and breather hose. P2772–P2774 split the fault types.

Symptoms

• Check engine light, often together with a flashing 4WD indicator
• Erratic speedometer or ABS warning when a speed signal is affected
• Low range not engaging, or transfer case disengaging under load

Most likely causes

• Loose tone wheel or moving output shaft in the transfer case (GM PIP4966B)
• Transfer case shift actuator damaged, e.g. by water through the breather (Toyota Tacoma)
• Low-range switch or position encoder defective
• Damaged wiring or corroded connector between switch and control module

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level and condition
2. With the connector unplugged, check whether the signal wire is making contact with ground.
3. Read the input and output speed in live data
4. Check the connector and wiring
5. Check for other related engine codes
6. Consult the manufacturer's procedure for the transmission

Good to know

• Repair difficulty: hard
• It can trigger limp mode.
• It affects emissions.

What each character of P2771 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 7: Transmission
• 71: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2771?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P2771?

The most common causes are: loose tone wheel or moving output shaft in the transfer case (GM PIP4966B); transfer case shift actuator damaged, e.g. by water through the breather (Toyota Tacoma); low-range switch or position encoder defective.

Related codes

• P2772Four Wheel Drive (4WD) Low Switch Circuit Range/Performance
• P2773Four Wheel Drive (4WD) Low Switch Circuit Low
• P2774Four Wheel Drive (4WD) Low Switch Circuit High
• P0836Four Wheel Drive (4WD) Switch Circuit
• P279BTransfer Case Gear Low Incorrect Ratio

Sources

• gsi.ext.gm.com: 16OBDG08 Transmission Diagnostics
• gsi.ext.gm.com: 14OBDG10 Engine Diagnostics
• static.nhtsa.gov: MC 10113036 9999
• static.nhtsa.gov: MC 11027561 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.