Code Definition

B1821 — Wiper Rear Motor Up Relay Coil Circuit Short To Ground

System: Body  |  Type: Manufacturer-Specific  |  Make: Ford

About B1821

B1821 is a manufacturer-specific body diagnostic trouble code recorded for Ford vehicles. It belongs to the B-prefix family of codes, which covers body, interior, airbag, or comfort-electronics faults.

When B1821 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

Scanning & clearing: Body (B) codes are often stored in the body control module, airbag module, or climate module. A basic OBD-II tool usually will not read body codes — an enhanced or OEM-level scan tool is typically required.

B1821 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Body Control Module (BCM) monitors the rear wiper motor up relay coil control circuit on Ford vehicles equipped with a rear wiper system. DTC B1821 is set when the BCM detects that the up relay coil control wire is shorted to ground, meaning the line is reading near 0V continuously instead of switching between battery voltage (relay off) and 0V (BCM commanding the relay on). A persistent ground on this line will hold the relay energised whenever supply voltage is present, or it can prevent the BCM from controlling the relay correctly depending on the strategy used. When this code is set, t...

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