Ignition
90-8M0050731 MAY 2011 Page 2A-15
Main Power Relay (MPR)
The main power relay (MPR) is located on the starboard side of the engine. The MPR is controlled by the PCM. After the first
system power up, the MPR is active for approximately five seconds. The PCM will deactivate the MPR unless the crankshaft
position sensor signals the PCM to initiate the MPR. The main power relay supplies 12 volts to the low‑pressure fuel pump,
high‑pressure fuel pump, oil pump, ignition coils, and the fuel injectors.
a - Main power relay (MPR)
Main Power Relay Test
The main power relay can be tested with the computer diagnostic system (CDS).
Computer Diagnostic System (CDS) Order through SPX
Adapter Harness 84‑822560A13
Extension Cable 84‑825003A 1
Use the DMT 2004 digital multimeter for all of the following tests.
DMT 2004 Digital Multimeter 91‑892647A01
1. Disconnect the engine harness from the main power relay.
2. Perform a visual inspection of the main power relay spade terminals. Look for loose or corroded spade terminals.
3. Measure the resistance between the main power relay coil terminals 85 (red/purple) and terminal 86 (yellow/purple). Replace
the relay if the resistance is not within the specifications.
Meter Test Leads
Meter Scale Reading (Ω)
Red Black
Terminal 85 Terminal 86 Auto ohms 85 ± 10 ohms
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