Main Relay

Main relay is part of relay module located at left side of engine compartment. See Fig 1 , Fig 2 or Fig 3 .

The main relay supplies power to the ECM, fuel injectors (8 amps) and Mass Airflow (MAF) sensor (4 amps). Relay is controlled by the ECM which has a second power feed. This enables the ECM to remain powered up after the ignition is turned off. During ECM power down, the ECM records all temperature readings and powers the IAC to the cold start position. Failure of this relay will result in the ECM not being powered up, resulting in engine not starting due to absence of fuel and ignition.

NOTE: Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the PCM. The second category covers OUTPUT SIGNALS, which are components controlled by the PCM.

Fig 1: Locating Computerized Engine Control Components (Defender 90)

Courtesy of LAND ROVER NORTH AMERICA, INC.

Fig 2: Locating Computerized Engine Control Components - Pre-Advanced EVAP (Discovery)

Courtesy of LAND ROVER NORTH AMERICA, INC.

Fig 3: Locating Computerized Engine Control Components - Advanced EVAP (Discovery)

Courtesy of LAND ROVER NORTH AMERICA, INC.