B1240

What Does Code B1240 Mean?

Diagnostic Trouble Code (DTC) B1240 indicates a specific electrical fault within the control circuit for the rear wiper washer pump relay. This code is typically categorized as a ‘B’ (Body) code, meaning it originates from a module responsible for chassis or body electrical functions, commonly the Body Control Module (BCM), Integrated Power Module (IPM), or a similar control unit, rather than the Powertrain Control Module (PCM). The control module monitors the resistance and voltage parameters of the relay’s coil circuit and its associated power and load circuits. When the module attempts to activate the rear washer function, it expects to see specific electrical feedback indicating the relay is properly switching current to the pump. If the module detects an abnormal condition—such as an open circuit (no current flow), a short to ground (excessive current/low voltage), or a short to voltage (unintended power)—within this critical circuit, it registers B1240. This signifies that the control module cannot reliably command or verify the proper operation of the rear washer pump relay, leading to a non-functional or intermittent rear washer system.

Common Symptoms

• Rear washer fluid does not spray when activated.
• No audible “click” from the relay when the rear washer function is commanded.
• Rear wiper may still operate normally, or in some cases, may become intermittent if the circuits are partially integrated.
• A warning message or indicator light related to the washer system may appear on the instrument cluster, though a Check Engine Light (CEL) is less common for B-codes unless specified by the manufacturer.

What Causes the Code B1240?

• Faulty Rear Wiper Washer Pump Relay: The relay itself may have internal failures such as an open coil, shorted contacts, or sticking contacts preventing it from energizing or switching current effectively.
• Wiring Harness Faults: An open circuit, short to ground, or short to voltage in the wiring between the control module and the relay, or between the relay and the washer pump. This includes chafed wires, broken conductors, or corroded/loose terminals within connectors.
• Defective Rear Wiper Washer Pump Motor: A shorted or open washer pump motor can create an abnormal load condition that the relay circuit cannot handle, leading the control module to interpret it as a relay circuit fault. A seized pump can also draw excessive current.
• Corrosion or Damage in the Fuse Box/Integrated Power Module (IPM): Poor contact or corrosion at the fuse holder for the rear washer pump relay, or internal damage within the fuse box/IPM where the relay is housed, can disrupt the circuit.
• Faulty Body Control Module (BCM): In rare instances, an internal fault within the BCM’s driver circuit for the rear washer pump relay can cause this code.

How to Diagnose and Troubleshoot

Diagnosis of B1240 requires a systematic approach using a digital multimeter (DMM) and an OBD-II diagnostic scanner:

1. Initial Visual Inspection: Begin by checking the rear washer fluid level. Visually inspect the entire wiring harness associated with the rear washer pump and relay. Look for any signs of physical damage, chafing, corrosion, or loose connections. Verify that all relevant fuses (refer to the vehicle’s service manual for location and rating, usually found in the under-hood or interior fuse box) are intact and have good contact.
2. OBD-II Scanner Check: Use a diagnostic scanner to confirm the presence of B1240 and check for any other related or historical codes. If the scanner has bi-directional control capabilities, attempt to activate the rear washer pump relay directly to see if it responds. Monitor any available live data stream from the BCM pertaining to the rear washer system or relay status.
3. Relay Testing:
   • Swap Test: If an identical, known-good relay (e.g., from the front washer system or another non-critical circuit) is available, swap it with the rear washer pump relay. If the problem resolves, the original relay is faulty.
   • Bench Test (Out-of-Circuit): Remove the rear washer pump relay. Use a DMM to measure the resistance across the relay’s coil terminals (usually 85 and 86). An open circuit (OL) or extremely low resistance indicates a faulty coil. Apply 12V to the coil terminals and check for continuity across the switch contacts (usually 30 and 87). A functional relay should click and show continuity.
4. Circuit Voltage and Continuity Checks (In-Circuit with DMM):
   • Power Supply to Relay: With the ignition in the RUN position, back-probe or use breakout box to check for 12V at the relay’s power input terminal (often terminal 30) using a DMM. This is the constant battery feed.
   • Ground to Relay Coil: Verify a good ground connection at one of the relay coil terminals (e.g., terminal 85 or 86, depending on the circuit design) using the DMM’s continuity or resistance function to chassis ground.
   • Control Signal to Relay Coil: With the DMM connected to the other relay coil terminal (e.g., terminal 86 or 85) and the ignition on, activate the rear washer function. The BCM should momentarily supply either 12V or ground to this terminal to energize the relay coil. The absence of this signal indicates a BCM or wiring issue on the control side.
   • Load Side to Pump: Check for continuity from the relay’s output terminal (e.g., terminal 87) to the positive terminal of the rear washer pump connector. With the relay commanded ON, check for 12V at the pump connector.
   • Washer Pump Motor Test: Disconnect the rear washer pump motor. Measure its internal resistance. An open circuit or a very low resistance (indicating a short) points to a faulty pump. You can also temporarily apply 12V and ground directly to the pump (briefly) to confirm its operation.
5. Wiring Integrity: If any voltage or continuity checks fail, use the service manual’s wiring diagrams to perform continuity tests on individual wires from the BCM connector to the relay connector, and from the relay connector to the pump connector. Check for shorts to ground and shorts to voltage on these circuits.

Recommended Repairs and Solutions

Based on diagnostic findings, the following repairs are typically recommended:

• Replace the Rear Wiper Washer Pump Relay: If testing confirms the relay is faulty, replace it with a new, OEM-specified relay. This is a common and often straightforward fix.
• Repair or Replace Damaged Wiring Harness: If damaged or corroded wiring, connectors, or terminals are identified, perform appropriate repairs. Use soldering and heat-shrink tubing for secure connections, or replace sections of the harness as needed. Ensure all connections are watertight and secure.
• Replace the Rear Wiper Washer Pump Motor: If the washer pump motor is determined to be faulty (e.g., shorted, open, or seized), replace it. Ensure proper fluid line connection and electrical hook-up. Prime the system if necessary after replacement.
• Clean or Replace Fuse/Fuse Holder: If a corroded or damaged fuse or fuse holder is causing an open circuit or high resistance, clean the contacts thoroughly or replace the fuse box component as necessary.
• Body Control Module (BCM) Replacement: Only consider BCM replacement as a last resort, after meticulously ruling out all other potential causes. BCM replacement is a complex procedure that often requires specialized programming or coding to the vehicle’s immobilizer and other systems, which should be performed by a qualified technician with appropriate diagnostic tools.