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Bobcat · Electrical

Bobcat code M6604: ECU no communication

What it means

The loader's main controller is not getting messages from the engine control unit (ECU). The machine may not start, or may shut down.

Can I keep running?

Stop: fix before running

No. Stop the machine safely (bucket or attachment down, engine off) and find the cause before you run it again.

Check first

  1. Park on level ground, lower the lift arms and attachment to the ground, stop the engine and remove the key.
  2. Check battery voltage, then clean and tighten the battery cables and ground straps. Bobcat notes that loose or corroded grounds can set several codes at once.
  3. Check the fuses and relays for that circuit using the fuse decal or the O&M manual.
  4. Look over the engine harness you can reach for rub-through, loose connectors or rodent damage.
  5. Restart and see if the code comes back. If it does, stop and call your Bobcat dealer.

Likely causes

  • Low battery voltage or a bad ground
  • Blown fuse or failed relay feeding the ECU
  • Loose, corroded or damaged wiring or connector between the ECU and the controller
  • Failed ECU (less common)

The fix

Power, ground and connector faults are the usual fix. If the basics check out, a dealer can test the ECU and the data link with Bobcat's service tool. Don't run the machine while the main controller can't see the engine.

Different code on your screen? Snap the display and Mechy reads it.

Related electrical codes

All Bobcat codes

Questions

What does Bobcat code M6604 mean?

ECU no communication. The loader's main controller is not getting messages from the engine control unit (ECU). The machine may not start, or may shut down.

Can I keep running with M6604?

No. Stop the machine safely (bucket or attachment down, engine off) and find the cause before you run it again.

How do I fix Bobcat code M6604?

Power, ground and connector faults are the usual fix. If the basics check out, a dealer can test the ECU and the data link with Bobcat's service tool. Don't run the machine while the main controller can't see the engine.

Sources

  1. Bobcat Company, Diagnostic Service Codes list (fault codes PDF, 2020)
  2. Bobcat T450 Operation & Maintenance Manual 7250077 (2018), Diagnostic Service Codes
  3. BigRentz, Full List of Bobcat Fault Codes (searchable table)

Code meanings vary by model, serial range and software. Confirm with your operator's manual or Bobcat dealer before replacing parts.

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