B1248

What Does Code B1248 Mean?

DTC B1248 signifies a detected electrical fault within the circuit of the passenger’s seatback autoglide rearward switch, specifically indicating a short to ground. While retrieved via the On-Board Diagnostic II (OBD-II) system, which primarily communicates with the Powertrain Control Module (PCM) or Engine Control Module (ECM) for powertrain-related issues, a ‘B’ prefix code denotes a fault within the vehicle’s body systems. For B1248, the monitoring is typically performed by the Body Control Module (BCM) or a dedicated Seat Control Module (SCM). This module constantly monitors the voltage and resistance characteristics of the autoglide switch circuit. When the module detects an unintended drop in voltage to near zero volts, indicating a direct connection to chassis ground, it identifies a short circuit and sets code B1248. This condition prevents the control module from accurately interpreting the switch’s intended state, thereby disabling or impairing the specific seat movement function. The subsystem affected is the passenger’s side power seat assembly, specifically the automated or comfort-assist seatback adjustment mechanism.

Common Symptoms

• Inoperative Passenger Seatback Rearward Autoglide Function: The primary symptom is the failure of the passenger seatback to move rearward using the specific autoglide switch.
• Intermittent Seat Adjustment Issues: Other seat adjustment functions, especially those controlled by the same module or power circuit, may experience intermittent operation.
• Illuminated Warning Lights: Depending on vehicle make and model, a general warning light, seatbelt indicator, or even an airbag light (if the seat position sensor is integrated or affected) might illuminate on the instrument cluster.
• Loss of Seat Memory Functions: If the autoglide function is integrated with a seat memory system, the ability to recall or save seat positions might be compromised.

What Causes the Code B1248?

• Damaged Wiring Harness: The most common cause is a compromised wire insulation within the passenger seatback autoglide switch circuit, allowing the wire to come into direct contact with the vehicle’s chassis or another ground source. This often occurs due to chafing, pinching, or wear from repeated seat movement.
• Faulty Passenger Seatback Autoglide Rearward Switch: An internal electrical short to ground within the switch assembly itself. This can be due to manufacturing defect, moisture ingress, or internal component failure.
• Corroded or Damaged Connector: Corrosion, bent pins, or foreign debris within the electrical connector leading to the switch or the seat control module can create a short to ground.
• Failed Seat Control Module (SCM) / Body Control Module (BCM): Less common, but an internal short within the controlling module (SCM or BCM) could cause the circuit to appear shorted to ground, even if the external wiring and switch are intact.

How to Diagnose and Troubleshoot

Diagnosis of B1248 requires a systematic approach, utilizing a diagnostic scan tool and a digital multimeter (DMM).

1. Retrieve and Document DTCs: Connect an OBD-II scan tool and retrieve all stored DTCs. Note freeze frame data if available, as it can provide valuable information about the vehicle’s operating conditions when the fault occurred. Clear the code and attempt to replicate the fault.
2. Perform a Thorough Visual Inspection:
   • Inspect the passenger seatback autoglide switch assembly for any physical damage, signs of water intrusion, or foreign objects.
   • Carefully examine the wiring harness leading to the switch, paying close attention to areas under the seat, near hinges, and where the harness might rub against seat frames or body components. Look for chafed, pinched, or exposed wires.
   • Inspect all related connectors for corrosion, loose terminals, or bent pins. Disconnect and reconnect them to ensure proper seating.
3. Utilize a Digital Multimeter (DMM):
   • Isolate the Switch: Disconnect the electrical connector from the passenger seatback autoglide rearward switch.
   • Check for Short to Ground in Harness: With the switch disconnected, set your DMM to resistance (Ohms). Place one lead on the suspected signal wire (refer to a wiring diagram for pinout) and the other lead on a known good chassis ground. A reading close to 0 ohms indicates a direct short to ground in the wiring harness. If the reading is infinite (OL), the harness is likely clear.
   • Test the Switch: If the harness tests clear, test the switch itself. Refer to the vehicle’s service manual for specific resistance values or continuity tests. Typically, with power applied to the switch, activating it should change the signal wire’s voltage. Without power, an internal short to ground in the switch would show a low resistance reading between the switch’s signal pin and its ground pin (or body).
   • Verify Power and Ground to the Switch: Using the DMM, check for proper power supply (usually 12V) and a good ground at the switch connector with the ignition ON. This ensures the switch is receiving necessary power.
4. Module Isolation (If Necessary): If the wiring harness and switch test clear, the issue might be internal to the Seat Control Module or Body Control Module. Disconnect the connector from the suspect module and re-test the circuit for a short to ground. If the short disappears with the module disconnected, the module itself may be at fault. This is a rare occurrence and should only be considered after exhaustive testing of the wiring and switch.

Recommended Repairs and Solutions

Based on the diagnostic findings, the appropriate repair typically involves:

• Repairing Damaged Wiring: If chafed or shorted wiring is identified, it should be carefully repaired. Use appropriate gauge wire, solder connections, and insulate with heat-shrink tubing to ensure a durable and factory-quality repair. Avoid electrical tape for permanent repairs.
• Replacing the Passenger Seatback Autoglide Rearward Switch: If the switch itself is found to have an internal short, it will need to be replaced with a new OEM or equivalent aftermarket part. Ensure the new switch is specific to the vehicle’s trim level and features.
• Cleaning or Replacing Connectors: If corrosion or damage is found in the connectors, use electrical contact cleaner and a small brush to clean terminals. For severe damage or bent pins, the connector housing or individual terminals may need to be replaced.
• Replacing the Seat Control Module (SCM) / Body Control Module (BCM): If all other components (wiring, switch, connectors) have been thoroughly tested and verified to be free of faults, and the module isolation test points to an internal module failure, the respective control module will need replacement. This often requires programming or coding with a specialized scan tool after installation.

Mechanic’s Tip: Always disconnect the vehicle’s battery negative terminal before performing any extensive electrical work under the seat to prevent accidental shorts or activation of airbag systems. After any repair, clear the DTCs and thoroughly test the passenger seat’s autoglide function multiple times to ensure the repair is complete and the code does not return.