Massey Ferguson 729.03 – Engine Control Unit (ECU): Engine Intake Heater High Voltage (ECU)

The Engine Control Unit (ECU) has detected a voltage in the intake air heater circuit that is above the normal specified range. This typically indicates an electrical fault, such as a short circuit to a power source or a malfunctioning relay that is stuck in the 'on' position, causing continuous voltage supply. The intake heater (grid heater) is designed to pre-heat air entering the intake manifold to aid in cold starting, reduce white smoke, and improve initial engine stability.

• 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
• 6713

1. 1

   Clear the code first: save the error log, erase it, and restart the ECU to rule out a transient voltage spike

2. 2

   Inspect the intake air heater relay and its electrical connections for damage, corrosion, or being stuck in the closed (ON) position

3. 3

   Inspect the grid heater wiring harness for defects, specifically looking for a short to a high voltage source

4. 4

   Check shared wiring: the intake air heater signal circuit shares wiring with the intake manifold pressure/temperature sensor, camshaft position sensor, water-in-fuel sensor, and rail fuel pressure sensor

1. 1

   Access components

   Turn off the engine and remove the engine hood assembly to access the intake manifold and relay block.

2. 2

   Locate relay

   Locate the intake air heater relay (usually found on the main fuse/relay block or near the intake manifold).

3. 3

   Test and replace relay

   Remove the relay cover and use a multimeter to test the relay for continuity. If the relay is stuck closed (providing constant high voltage to the heater), replace the relay.

4. 4

   Inspect and repair wiring

   If the relay is functioning correctly, trace the wiring from the relay to the intake air heater (grid heater) on the intake manifold. Repair or replace any sections of the harness that are melted, chafed, or shorted to power.

5. 5

   Replace intake air heater

   If the wiring and relay are both intact and functioning properly, the fault lies within the intake air heater itself. Remove the intake hose and electrical connections to the grid heater, unbolt it from the intake manifold, and install a replacement unit.

6. 6

   Verify repair

   Clear the fault codes via the diagnostic port and run the engine to verify the repair.