COMPONENT LOCATION
GENERAL DESCRIPTION

Fuel metering unit(MPROP) is integrated with high pressure pump and controls common rail pressure as regulating the quantity of fuel which is delivered to common rail. In order to control rail pressure to be optimum to current driving condition, ECM controls fuel pressure regulator operating current(with the method of duty-control) using RPCV signal, RPM and APS signal.The lower Fuel metering unit current is, the more fuel is supplied to common rail. Thus it leads rail pressure to be high. On the contrary, the higher Fuel metering unit current is, the less fuel is supplied to common rail. Thus it leads rail pressure to be low. Therefore, when Fuel metering unit current becomes "0", as if there is open spot in Fuel metering unit circuit or connector is disconnected, maximum fuel quantity is supplied to common rail, so the pressure of common rail rise to maximum value.

DTC DESCRIPTION

P0253 is set when "0"A in control circuit of Fuel metering unit(integrated with high pressure pump) is detected for more than 0.22 sec.. This code is due to open of short to ground in control circuit or Fuel metering unit internal open.

DTC DETECTING CONDITION

Item

Detecting Condition

Possible Cause

DTC Strategy

●

Voltage monitoring

●

FMU circuit

●

FMU component

Enable Conditions

●

IG KEY "ON"

ThresholdValue

●

Short to GND, Wiring open

DiagnosticTime

●

220ms

Fail Safe

Fuel Cut

NO

EGR Off

NO

Fuel Limit

YES

MIL

YES

SPECIFICATION

rail pressure control valve resistance

Operating frequancy

2.9 ~ 3.15Ω (20℃)

185 Hz

SCHEMATIC DIAGRAM
SIGNAL WAVEFORM AND DATA
MONITOR SCANTOOL DATA
1.

Connect Scantool to Data Link Connector (DLC).

2.

Warm engine up to normal operating temperature.

3.

Turn "OFF" electrical devices and A/C.

4.

Monitor "FUEL PRESSURE MEASURED", "RAIL PRESS. REGULATOR1", "INJ. PUMP REGULATOR" parameter on the Scantool.

Specification :

Idle(without load)

Accelerating(stall test)

Diagnosis

INJ. PUMP REGULATOR

38 ± 5%

32 ± 5%

duty decreases

FUEL PRESSURE MEASURED

28.5 ± 5 Mpa

145 ± 10 Mpa

press. increases

RAIL PRESS. REGULATOR1

19 ± 5%

48 ± 5%

duty increases

note

The waveform of fuel metering unit installed at high pressure pump(fuel detecting MPROP) shows 38% duty at idle, duty drops to approx. 32% at acceleration to raise rail pressure. Duty drop means the decrease of current.

→ Fuel delivered to common rail increases as current drops.

The waveform of rail pressure control valve installed at common rail shows 19% duty at idle, duty rises to approx. 48% at acceleration to raise rail pressure. Duty rise means the increase of current.

→ If current rises, the returning quantity of fuel deliverd to common rail decreases and common rail pressure rises.

TERMINAL AND CONNECTOR INSPECTION
1.

Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.

2.

Perform checking procedure as follows.

(1)

Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.

(2)

Check connecting condition of ECM and component connector : Check terminal seperation, damage of locking device and connecting condition between terminal and wiring.

note

Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )

3.

Is the problem found?

▶ Repair the trouble causing part and go to "Verification of Vehicle Repair".

▶ Go to "Power Circuit Inspection".

POWER CIRCUIT INSPECTION
1.

Check power circuit voltage

(1)

IG KEY "OFF", ENGINE "OFF".

(2)

Disconnect FMU connector.

(3)

IG KEY "ON".

(4)

Measure the voltage of FMU connector terminal 1.

specification : 11.5V~13.0V

(5)

Is the measured voltage within the specification?

▶ Go to "Control Circuit Inspection".

▶ Repair open between FMU connector terminal 1 and ECM connector terminal 19 and go to "Verification of Vehicle Repair".

CONTROL CIRCUIT INSPECTION
1.

Check monitoring voltage in control circuit

(1)

IG KEY "OFF", ENGINE "OFF".

(2)

Disconnect FMU connector.

(3)

IG KEY "ON".

(4)

Measure the voltage of FMU connector terminal 2.

specification : 3.2V~3.7V

(5)

Is the measured voltage within the specification?

▶ Go to "Component Inspection"

▶ When voltage is not detected : Go to "2. Check open in control circuit" as follows.

▶ When high voltage is detected : Repair short to battery and go to "Verification of Vehicle Repair".

2.

Check open in control circuit

(1)

IG KEY "OFF", ENGINE "OFF".

(2)

Disconnect FMU and ECM connector.

(3)

Check continuity between FMU connector terminal 2 and ECM connector terminal 49.

specification : Continuity ( below 1.0Ω )

(4)

Is the measured resistance within the specification?

▶ Repair short to ground in FMU control circuit and go to "Verification of Vehicle Repair".

▶ Repair open in FMU control circuit and go to "Verification of Vehicle Repair".

COMPONENT INSPECTION
1.

Check FMU component resistance

(1)

IG KEY "OFF", ENGINE "OFF".

(2)

Disconnect rail pressure control valve connector.

(3)

Check FMU component resistance.

Specification : 2.9 ~ 3.15Ω (20℃)

(4)

Is FMU component resistance within the specification?

▶ Go to "Verification of Vehicle Repair".

▶ Replace High pressure pump ass'y and go to "Verification of Vehicle Repair".

VERIFICATION OF VEHICLE REPAIR

After a repair, it is essential to verify that the fault is corrected.

1.

After connecting Scantool select "DIAGNOSTIC TROUBLE CODES(DTCs)" mode.

2.

Clear recorded DTC using Scantool.

3.

Drive the vehicle within DTC "Enable conditions" in "General information".

4.

After selecting "DIAGNOSTIC TROUBLE CODES(DTCs)" mode and check if DTC is recorded again.

5.

Are any DTCs recorded ?

▶ Go to the DTC guide of recorded NO. in Scantool.

▶ System operates within specification.

Яндекс.Метрика