What Does B1388 Mean?
This code indicates the Body Control Module (BCM) or Powertrain Control Module (PCM) has detected a short to battery voltage in the oil temperature sensor circuit. The sensor's signal wire is making unintended contact with a voltage source, causing the circuit to read constant high voltage instead of the normal variable resistance signal from the sensor. This prevents accurate monitoring of engine or transmission oil temperature.
Common Causes
45%
Damaged or chafed wiring harness causing short to power wire
30%
Failed oil temperature sensor with internal short to voltage
15%
Corroded or damaged connector pins creating cross-circuit short
10%
Control module internal fault causing false detection
Diagnostic Steps
1
Step 1: Perform visual inspection of oil temperature sensor wiring harness from sensor to control module, looking for chafing, pinching, melted insulation, or contact with hot components. Pay special attention to areas where harness passes near battery cables or other power sources.
2
Step 2: Disconnect oil temperature sensor connector and measure resistance between sensor signal pin and ground using a digital multimeter. Typical sensors read 2000-5000 ohms at room temperature. If open circuit or out of range, sensor is faulty.
3
Step 3: With sensor disconnected, check for voltage on the sensor signal wire at the harness connector using multimeter. Should read 0-5V reference voltage, not battery voltage (12V+). If battery voltage present, trace wiring for short to power.
4
Step 4: Inspect sensor connector terminals for corrosion, bent pins, or moisture intrusion. Check connector for proper seating and locking mechanism engagement. Clean or replace connector if damaged.
5
Step 5: If wiring and sensor test good, measure resistance of sensor signal circuit from sensor connector to control module with all connectors disconnected. Should read less than 5 ohms. High resistance indicates wiring damage.
6
Step 6: After repairs, clear codes and perform drive cycle monitoring oil temperature readings with scan tool to verify sensor operates within normal range (typically 150-250°F operating temp) and code does not return.
Estimated Repair Cost
$100 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) or Powertrain Control Module (PCM) has detected a short to battery voltage in the oil temperature sensor circuit. The sensor's signal wire is making unintended contact with a voltage source, causing the circuit to read constant high voltage instead o...
The most common cause of B1388 (Oil Temperature Sensor Circuit Short To Battery) is: Damaged or chafed wiring harness causing short to power wire
Typical repair costs for B1388 range from $100 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is generally safe to drive short distances, but the control module cannot properly monitor oil temperature which may result in inadequate protection against overheating or poor transmission shift quality. Avoid extended driving or heavy loads until repaired to prevent potential engine or transmission damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1388 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Body
System
Engine Management System / Transmission Control System
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
