What it means
Transmission Mode Switch A Circuit: an electrical fault is present in the circuit.
At a glance
- Usually lights the check-engine light
How it works
Transmission mode switch A reports the selected operating mode to the TCM. P071A sets when the switch A circuit has an electrical fault or its signal does not change as expected, so the TCM may not recognize the driver's selected transmission mode.
Common causes
Most likely first.
- Faulty transmission mode switch A
- Open or short in switch wiring
- Poor connector contact or corrosion
- Misadjusted or damaged switch
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and check scan-tool data for the mode reported by switch A while selecting each available transmission mode.
- Inspect switch A's connector and wiring for corrosion, loose or pushed-back pins, damage, and poor routing near moving parts.
- Check whether the switch is correctly positioned and mechanically moves with the selector, using the manufacturer's adjustment procedure.
- Test the switch A circuit for opens, shorts, and continuity in each switch position using the manufacturer's wiring diagram.
- If wiring and adjustment pass, test transmission mode switch A itself against the manufacturer's specification.
Common fixes
- Clean and secure the mode switch A connector if contact is poor.
- Repair damaged, open, or shorted wiring in the switch A circuit.
- Adjust or reposition switch A if it is misaligned and the specified procedure permits it.
- Replace transmission mode switch A if its output is faulty.
- Replace damaged connector terminals or repair selector linkage if inspection identifies the cause.
Can I keep driving?
If the selected mode is unclear or the transmission shifts unpredictably, avoid driving and arrange assistance. If it selects and shifts normally, drive cautiously and avoid towing or strenuous use until switch A is repaired.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.