Transmission Mode Switch Circuit Low
The P071B code indicates that the Powertrain Control Module (PCM) has detected a low voltage condition in the transmission mode switch circuit. This switch, often part of the manual shift or sport mode selector, sends a signal to the PCM to change shift patterns. A low circuit voltage suggests a short to ground, open circuit, or faulty switch, potentially causing incorrect transmission operation.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in default or limp mode
- Inability to select manual/sport mode
- Harsh or erratic shifting
- Reduced fuel economy
2. Most Common Causes
- Faulty transmission mode switch
- Short to ground in the switch circuit
- Open or damaged wiring/connectors
- Corroded or loose electrical connections
- Failed PCM (rare)
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect the transmission mode switch and wiring for damage, corrosion, or loose connections.
Step 3: Test the switch resistance and voltage with a multimeter; compare to manufacturer specs.
Step 4: Check for shorts to ground or opens in the circuit between the switch and PCM.
Step 5: If all else is good, test the PCM for proper operation or update software.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the transmission may enter limp mode, causing reduced performance and potential damage. Have it diagnosed promptly.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and repair, but costs can vary if the switch or PCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.