What Does P071B Mean?
The transmission mode switch A circuit is reporting a low voltage condition. This typically means the signal line is shorted to ground, the switch is stuck in one position producing a low output, or there is a wiring fault pulling the signal low. The TCM may be unable to detect mode changes requested by the driver.
Common Causes
35%
Mode switch shorted internally or stuck in low-voltage position
25%
Signal wire shorted to ground in the harness
20%
Corroded or contaminated switch connector creating a ground path
10%
Liquid spill damage to the mode switch assembly
10%
TCM internal pull-down fault on the switch input
Diagnostic Steps
1
Monitor the mode switch A voltage PID. If it reads near 0V regardless of switch position, the circuit has a low/ground condition.
2
Disconnect the mode switch connector. If the voltage rises to reference level, the switch is shorted. If it stays low, the harness has a short to ground.
3
Inspect the switch assembly for liquid damage, corrosion, or physical damage. Disassemble the center console area if needed to access the switch.
4
Measure resistance between the signal wire and ground at the switch connector — should be open (OL) with the switch disconnected. A low reading confirms a harness short.
5
If the switch and harness test OK, check the TCM connector for the mode switch input pin. Verify it is not shorted to an adjacent ground pin.
Estimated Repair Cost
$50 - $300
Parts + labor, varies by vehicle and location
The transmission mode switch A circuit is reporting a low voltage condition. This typically means the signal line is shorted to ground, the switch is stuck in one position producing a low output, or there is a wiring fault pulling the signal low. The TCM may be unable to detect mode changes requeste...
The most common cause of P071B (Transmission Mode Switch "A" Circuit Low) is: Mode switch shorted internally or stuck in low-voltage position
Typical repair costs for P071B range from $50 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. The transmission operates normally in its default mode. You simply lose the ability to switch between driving modes. Repair when convenient.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P071B to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Generic (SAE)
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