Deutz-Fahr I37 – Instrument Panel (Dash): Relay fault within the engine preheating (glow plug) circuit

The instrument panel detects that the preheating device is off when it is commanded to be on, or that the preheating control relay is disconnected or short-circuiting to ground.

• Agroplus 310, 320, 410, and 420 Profiline series tractors
• Agrofarm 85
• Agrofarm 100
• Agrofarm 410
• Agrofarm 420
• Agrofarm 430
• Agrotron
• Agroplus
• 5C series
• 5G series
• 6C series

1. 1

   Visually inspect the contacts on connector '5K' at the instrument panel and connector 'RL42' at the preheating control relay for oxidation or corrosion.

2. 2

   Perform a continuity test between pin 2 of connector 'RL42' and pin 19 of connector '5K' (should read 0 Ohms).

3. 3

   Test the circuit for continuity to the chassis ground to rule out a shorted wire harness.

4. 4

   Bench test the preheating control relay (RL42) by applying 12V to the coil pins and verifying that the load contacts close with minimal resistance.

1. 1

   Disconnect Power

   Disconnect the battery terminals (negative terminal first) before working on the tractor's electrical system to prevent short circuits.

2. 2

   Access the Components

   Remove the necessary dash trim to access the rear of the instrument panel (Connector 5K) and the relay panel to access the preheating control relay (RL42).

3. 3

   Clean Contacts

   If oxidation was found during the diagnostic checks, use a dedicated electrical contact cleaner to clean the pins on both the relay socket and the instrument panel connector.

4. 4

   Repair Wiring

   If the continuity test failed, trace the wire between pin 19 of the dash and pin 2 of the relay. Repair any chafed, broken, or melted sections of the harness.

5. 5

   Replace the Relay

   If the wiring is intact but the relay failed the bench test (or if the internal coil is shorted to ground), replace relay RL42 with a new OEM unit.

6. 6

   Reassembly and Clearing Codes

   Reconnect all plugs, then reconnect the battery (positive first, then negative). Clear all alarms from the dash.

7. 7

   Verify Repair

   Turn the starter key to 'I' (ON) while the engine is cold (below 30°C) and verify that the preheating light illuminates and the relay clicks on without triggering the I37 code.