B1816 — Wiper Rear Motor Down Relay Coil Circuit Short To Battery #

The code label may vary depending on the vehicle manufacturer (OEM). Below are known variations of this code’s description:

• B1816: Rear Wiper Motor Down Relay Shorted to Battery (Ford)
• B1816: Rear Wiper Down Relay Circuit High (General Motors)
• B1816: Rear Window Wiper Motor Down Relay Input Circuit High (Toyota)

Summary of Code B1816 #

The B1816 diagnostic trouble code (DTC) is triggered when the vehicle’s onboard computer—commonly referred to as the Body Control Module (BCM)—detects that the electrical circuit controlling the rear wiper motor’s “down” relay coil is shorted to battery voltage. In simple terms, this means the wire or component intended to activate the rear wiper in the downward position is receiving constant voltage when it shouldn’t. This anomaly can confuse the system and result in erratic rear wiper behavior or complete inoperability. The code is specific to the rear wiper system’s relay circuit and typically points to an electrical fault—often a wiring or relay problem—rather than a mechanical one. Prompt diagnosis is recommended to avoid further electrical issues or inconvenience during adverse weather.

Common Symptoms for Code B1816 #

Drivers and technicians may notice several symptoms when this code is present. These can range from subtle quirks to outright failure of the rear wiper system. Here’s what you might experience:

• Rear wiper does not operate in the “down” position
• Wiper runs continuously or at random intervals when not commanded
• Wiper stops mid-cycle or does not park correctly
• Rear wiper system warning light or message on the dashboard (if equipped)
• Possible blown fuse related to the rear wiper circuit

Probable Causes for Code B1816 #

The B1816 code is most often traced to electrical faults rather than mechanical component failure. The possible causes, listed from most to least common, include:

1. Short to battery voltage in the rear wiper relay coil circuit wiring (damaged, frayed, or pinched wire contacting a voltage source)
2. Faulty rear wiper down relay (internal short or stuck contacts)
3. Corroded or contaminated relay socket (bridging power to the relay coil unintentionally)
4. Faulty Body Control Module (BCM) (rare, but possible if all other possibilities are eliminated)
5. Incorrect installation of aftermarket electrical accessories causing unintended power feed into the circuit

Step-by-Step Diagnosis for Code B1816 #

Accurately diagnosing the B1816 code requires a systematic approach to avoid unnecessary parts replacement. Here’s a recommended diagnostic path:

• Verify the code using an OBD-II scan tool and note any related codes.
• Inspect the rear wiper relay and its socket for signs of damage, corrosion, or melting.
• Check the wiring harness from the BCM to the rear wiper relay for pinched, frayed, or exposed wires—especially where the harness runs through the tailgate or hatch.
• Test the relay by swapping it with a known good unit (if possible) or bench-testing for internal shorts between the coil and power terminals.
• Measure voltage at the relay coil circuit with the ignition on (but wiper off); voltage present when it shouldn’t be indicates a short to battery.
• If all checks pass, inspect the BCM’s output pin for the rear wiper down relay for internal failure.
• Clear the code, cycle the ignition, and retest to confirm the fix.

Possible Repairs for Code B1816 #

Depending on the cause found during diagnosis, several repair options exist for B1816. Always address the root cause rather than simply clearing the code.

• Repair or replace damaged wiring in the rear wiper relay coil circuit
• Replace the rear wiper down relay if found faulty
• Clean or replace the relay socket if corrosion or contamination is present
• Re-route or shield wiring if physical interference is causing shorts
• Replace the BCM only if it’s conclusively proven to be faulty, and after all other steps
• Remove or correct any aftermarket electrical modifications interfering with the circuit

Is It Safe to Drive with Code B1816? #

Yes, you can usually drive with this code, but with limitations. The B1816 code does not typically affect critical engine or safety systems. However, your rear wiper may not function or may behave unpredictably. This can be a significant safety concern in rain or snow, especially if rearward visibility is crucial. If you rely on your rear wiper, address the issue promptly. Otherwise, avoid driving in conditions where you need to see through the rear window until it’s fixed.

Vehicles Most Commonly Affected by Code B1816 #

While this code can appear on any vehicle with a rear wiper system using relay control, it is most commonly reported on certain models. These include:

• Ford Escape, Expedition, Explorer, and Flex
• Chevrolet Traverse, Equinox, and Tahoe
• Toyota RAV4 and Highlander
• Honda CR-V
• Dodge Grand Caravan
• Nissan Rogue

Frequent Errors & Best Practices for Code B1816 #

Mistakes in diagnosing or repairing B1816 often lead to wasted time and money. Here’s what to watch out for and how to proceed smartly:

• Replacing the wiper motor unnecessarily—remember, this is a relay circuit issue, not a motor failure code.
• Overlooking hidden wiring damage, especially where harnesses flex with hatch or tailgate movement.
• Not checking for aftermarket wiring (alarms, cameras, etc.) that may have introduced a short.
• Neglecting to inspect the relay socket for corrosion or debris.
• Failing to clear the code and retest after repairs, which can mask an intermittent problem.

Express FAQ for Code B1816 #

Here are quick answers to common questions about the B1816 code:

• Q: Will this code drain my battery?
  A: If the relay or circuit is stuck powered, it could cause the wiper motor or relay to draw current continuously, leading to battery drain over time if the vehicle is left parked.
• Q: Can I just pull the rear wiper fuse to stop odd behavior?
  A: Yes, removing the fuse will disable the rear wiper system. However, this is a temporary workaround and not a true fix for the underlying electrical problem.