MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS
TSB Revision
MULTIPORT FUEL INJECTION (MFI)
13A-773
• When the fuel pump relay 2 is turned ON, the fuel
pump drive power is supplied from the fuel pump
relay 2 (C-314 ETACS-ECU connector terminal
No. 1) to the fuel pump (terminal No. 5).
• When the vehicle is driven at low engine loads,
the ECM (terminal No. 51) turns OFF the power
transistor of the unit. The current is not going
through the fuel pump relay 1, and then the relay
is turned OFF.
• When the vehicle is driven at high engine loads,
the ECM (terminal No. 51) turns ON the power
transistor of the unit. The current is going through
the fuel pump relay 1 (terminal No. 1), and then
the relay is turned ON. Thus the fuel pump drive
power is supplied from the fuel pump relay 1 (ter-
minal No. 3) to the fuel pump relay 2 (C-307
ETACS-ECU connector terminal No. 1).
.
COMMENT
• The ECM turns ON the fuel pump relay 2 during
the engine cranking and running, and then sup-
plies the drive power to the fuel pump.
• The ECM supplies the drive power to the fuel
pump via the resistor during the engine running at
low engine loads. The ECM supplies the drive
power directly to the fuel pump during the engine
running at high engine loads to increase the fuel
discharge rate of fuel pump.
.
TROUBLESHOOTING HINTS (The most
likely causes for this case:)
• Malfunction of the fuel pump relay 1.
• Malfunction of fuel pump relay 2 of ETACS-ECU.
• Malfunction of the fuel pump.
• Malfunction of the fuel pump circuit resistor.
• Improper connector contact, open or short-circu-
lated harness wire.
• Malfunction of the ECM.
DIAGNOSIS
Required Special Tools:
• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
• MB991824: V.C.I.
• MB991827: USB Cable
• MB991910: Main Harness A
STEP 1. Check harness connector C-304, C-307, C314 and
C-317 at ETACS-ECU for damage.
Q: Is the connector in good condition?
YES : Go to Step 2.
NO : Repair or replace it. Refer to GROUP 00E, Harness
Connector Inspection
P.00E-2
. Then confirm that the
malfunction symptom is eliminated.