Massey Ferguson 729.04 – Engine Control Unit (ECU): Engine Intake Heater Low Voltage (ECU) / Grid Heater Voltage Below Normal

The engine control module has detected that the voltage on the intake air heater (grid heater) signal circuit is below normal or shorted to a low source (ground). This typically indicates a short circuit to ground in the wiring harness, a failed grid heater relay, or an internally shorted intake heater element.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724

1. 1

   Inspect the wiring harness running from the ECU to the grid heater relay, and from the relay to the intake heater element on the manifold for chafed insulation, bare wires rubbing against the engine block, or melted connectors.

2. 2

   Disconnect the grid heater connector and turn the ignition key to the ON position (engine OFF). Check the diagnostic tool; if the code changes from 000729.04 to an open circuit code (like FMI 5), the short is inside the heater element itself.

3. 3

   Test the 70 Amp grid heater relay. A fused or internally shorted relay can pull the voltage down and trigger this code.

4. 4

   Use a multimeter to measure the resistance of the intake heater element to ground. If it shows continuity to the manifold housing (zero resistance), the element is shorted.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery cable to prevent accidental arcing or ECU damage during repair.

2. 2

   Access the Components

   Locate the intake air heater on the engine intake manifold and trace its wiring back to the 70 Amp starter/grid heater relay.

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed a chafed wire shorting to the chassis, repair the wire using heat-shrink connectors and re-loom the harness to prevent future rubbing.

4. 4

   Replace the Relay (If Applicable)

   If the relay failed testing, unbolt the old relay, transfer the wiring to the new 70 Amp relay, and secure it to the firewall/bracket.

5. 5

   Replace the Intake Heater (If Applicable)

   Disconnect the heavy-gauge electrical cable from the top of the intake heater element. Unbolt the intake heater from the intake manifold. Clean the mating surfaces on the manifold to ensure a good seal. Install the new intake air preheater and torque the mounting bolts to OEM specifications. Reattach the electrical cable securely.

6. 6

   Clear Codes

   Reconnect the battery, turn the ignition ON, and use a diagnostic scan tool to clear the 000729.04 fault code. Start the engine and verify the code does not return.