A 2005 Ford Mustang GT is experiencing a no-communication issue after a fuel pump relay modification. The owner attempted to use the #41 relay (fuel pump relay) to power an aftermarket fan by inserting a wire into the relay. This action blew the fuel pump fuse. Replacing the fuse and relay did not resolve the issue, and the fuel pumps remain inoperative.
Further investigation revealed that using a jumper wire in the #41 relay slot also failed to activate the fuel pumps. However, directly powering the fuel pumps confirmed their functionality. Power is present at the fuel pump hat connection, indicating a lack of activation signal.
Subsequent tampering resulted in a complete loss of communication. With the relay in the #41 slot, the throttle body does not actuate with the key in the forward position. Using a jumper wire restores throttle body actuation. Additionally, an SCT tuner no longer connects to the vehicle’s computer, displaying error code 21000. The battery was previously dead but has since been charged. Prior to these modifications, the car started and communicated with the SCT tuner without issue.
The primary concern is the lack of communication, indicated by the Obdii Code 21000 and the SCT tuner connection failure. This suggests a potential problem with the vehicle’s computer (ECU) or a critical wiring issue within the fuse box. The initial fuel pump problem may be related to the broader communication failure.
Several potential causes should be investigated:
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Damaged Wiring: The improper use of the #41 relay could have damaged wiring within the fuse box or related circuits, disrupting communication between critical components.
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Faulty Fuse Box: The fuse box itself may have sustained damage due to the electrical fault, affecting various systems and communication pathways.
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ECU Malfunction: The ECU may have been damaged by the electrical issue, leading to the communication breakdown and error code 21000.
Troubleshooting steps should include a thorough inspection of the fuse box and related wiring for damage, testing of critical fuses and relays, and checking for proper grounding. If no visible damage is found, professional diagnostics may be necessary to pinpoint the source of the communication failure and determine if the ECU requires replacement or repair.
The OBDII code 21000 and associated symptoms indicate a serious electrical issue affecting communication within the vehicle’s systems. Addressing the potential causes systematically, starting with the fuse box and wiring, is crucial to restoring functionality.
