B1388: EOT/TFT Sensor Circuit High Voltage
The B1388 code indicates that the Powertrain Control Module (PCM) has detected an excessively high voltage (short to battery or reference voltage) in the signal circuit of the Engine Oil Temperature (EOT) or Transmission Fluid Temperature (TFT) sensor. This prevents accurate temperature readings, disabling thermal protection strategies and shift control logic.
1. Commonly Affected Makes
2. Most Common Causes
- Internal short to voltage in the EOT or TFT sensor
- Signal wire shorted to a power source (VPWR or battery)
- Damaged sensor connector with bent pins or corrosion bridging signal and power terminals
- Rare internal PCM failure in the sensor input circuit
3. Symptoms You Will Notice
- Check Engine Light or Transmission Warning Light illuminated
- Harsh or erratic transmission shifts
- Reduced fuel economy
- Possible limp mode or reduced engine power
4. Step-by-Step Diagnosis
Scan for additional codes and verify B1388 is present
Visually inspect the EOT/TFT sensor connector for damage, corrosion, or bent pins
Measure voltage at the sensor signal wire with key on; should be near 0V when cold. If battery voltage is present, suspect a short to power
Disconnect the sensor and check if voltage drops to 0V; if not, repair the short in the wiring harness
Test sensor resistance per manufacturer specs; replace if out of range
If all checks pass, suspect a PCM fault (rare) and perform a PCM self-test or replacement
5. Frequently Asked Questions
Is it safe to drive?▼
No, driving with this code is not recommended. The PCM disables thermal protection and shift strategies, which can lead to transmission damage or engine overheating.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the sensor ($30-$100) or wiring repair is needed. PCM replacement can exceed $800.