Powertrain, generic · Transmission
P071B Transmission Mode Switch A Circuit Low
Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo
A transmission mode switch selects an alternative shift schedule such as sport, winter or tow/haul; J2012 does not define which button is A or B. No manufacturer document available to us uses P071A–P071F: GM monitors its analog drive mode switch under its own codes (low below 21–29 % of 5 V, high from 94 %, 200 of 250 samples, two trips), which shows how such buttons are read as coded voltages. P071B means the signal of mode switch A is below its lower limit: with analog, resistor-coded buttons a short to ground, with digital buttons switching to ground a button stuck pressed. The opposite is P071C.
Likely causes
Signal wire shorted to ground
Button stuck pressed (switching to ground)
Moisture or dirt in the button
Control module faulty
Symptoms
- Mode A cannot be selected or stays active
- Mode indicator missing or flashing
- Transmission stays on the normal shift schedule
Repair estimate
DifficultyEasyDIY possible
Parts and labour€30–300
Time0.3–1.5 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
transmission mode switchswitch wiringtransmission control module
Related codes
References: law.cornell.edu, gsi.ext.gm.com.