The B1820 OBD2 fault code relates to the Wiper Rear Motor Up Relay Coil circuit. When the circuit short to battery, the module cannot properly monitor or control this body system.
At AIscanAuto, we help drivers quickly identify OBD2 trouble codes, understand their root causes, and find the right fix.
Symptoms
- Wiper not working or erratic operation
- Washer pump not activating
- Possible warning indicator
- Intermittent wiper failure
Common Causes
- Faulty component — internal damage or wear affecting Wiper Rear Motor Up Relay Coil
- Wiring issues — broken, corroded, or chafed wires in the circuit
- Connector problems — loose, oxidized, or moisture-damaged pins
- a short to battery voltage is detected — connects the signal line directly to 12V, causing constant high voltage
- Module input failure — rare, but the control module input stage may be defective
Step-by-Step Diagnosis
- Scan with OBD2 tool — Confirm B1820 is active. Check for additional DTCs.
- Visual inspection — Examine the Wiper Rear Motor Up Relay Coil wiring and connector for corrosion or damage.
- Check voltage and ground — Use a multimeter to verify proper reference voltage.
- Test component — Compare readings to factory specs. A stuck or erratic signal confirms failure.
- Check for shorts/opens — Perform continuity tests on the wiring between the component and control module.
Repair & Solutions
- If the component is defective, replace the Wiper Rear Motor Up Relay Coil with an OEM or quality aftermarket part.
- Repair any damaged wiring or connectors using proper methods.
- Clear the DTC with an OBD2 scanner and test drive to verify the code does not return.
- If the code persists after component replacement, inspect the control module connector.
Related Codes
- B1817 — Wiper Rear Motor Down Relay Coil Circuit Short To Ground
- B1818 — Wiper Rear Motor Up Relay Coil Circuit Failure
- B1819 — Wiper Rear Motor Up Relay Coil Circuit Open