Content .. 85 86 87 88 ..

Isuzu engine C22NE / 22LE / 20LE. Manual - part 87

DRIVEABILITY AND EMISSIONS 6E1-177

0.5

YEL/

GRN

0.5

GRN

0.5

RED

0.5

RED

0.5

GRN

0.5

RED

Manifold

Absolute

Pressure

(MAP)

Sensor

F10

0.5

GRN

5 Volt

Reference

Signal

MAP Sensor

Input

Sensor

Ground

0.75

A B

Intake

Air Temperature

Sensor

Throttle Position

Sensor

Engine

Control

Module

(ECM)

OUT

0.5

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 34)

MANIFOLD ABSOLUTE PRESSURE (MAP) TOO LOW

Circuit Description

The manifold absolute pressure (MAP) sensor

responds to changes in intake manifold pressure. The

MAP sensor signal voltage to the engine control

module (ECM) varies from below 2 volts at idle (low

manifold pressure) to above 4 volts with the ignition

ON engine not running or at wide-open throttle (high

manifold pressure).

A "speed density" method of determining engine load

is used. This is calculated using inputs from the MAP

sensor, the CKP Sensor, and the Intake Air

Temperature (IAT) sensor. The MAP sensor is the

main sensor used in this calculation, and measuring

engine load is its main function. The ECM monitors

the MAP signals for voltages outside the normal range

(10-104 kpa) of the MAP sensor. If the ECM detects a

MAP signal voltage that is excessively low, Diagnostic

Trouble Code 34 will be set.

Conditions for Setting the DTC

• Manifold Absolute Pressure is less than 14 kpa and

one of following condition is met the DTC will set.

Condition A:

• Malfunction 21 not present and rpm is less than

1050.

Or,

Condition B:

• Malfunction 21 not present and rpm is greater

than 1050 and TP opening is greater than

18.75% and ignition ON.

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL).

Conditions for Clearing the MIL/DTC

Once the ECM determines that a fault(s) has been

rectified then the CEL will switch OFF, although the

fault code will remain in the ECM memory.

Any fault codes will remain in ECM memory until -

6E1-178 DRIVEABILITY AND EMISSIONS

1. They are cleared by disconnecting the Battery for

more than 30 seconds.

2. A service tool such as Tech 2 is used to clear them.

3. Ten consecutive starts without logging a fault.

Diagnostic Aids

Check for the following conditions:
• Poor connection at ECM - Inspect harness

connectors for backed-out terminals, improper

mating, broken locks, improperly formed or

damaged terminals, and poor terminal-to-wire

connection.

• Damaged harness - Inspect the wiring harness for

damage, shorts to Ground, shorts to Battery

positive, and Open circuits. If the harness appears

to be OK, observe the MAP display on the Scan

Tool while moving connectors and wiring harnesses

related to the sensor. A change in the display will

indicate the location of the fault.

• A faulty 5 volt reference circuit could also set a TP

Sensor Diagnostic Trouble Code because the two

sensors share the same 5 volt reference pin at the

ECM.

DTC (Flash DTC = 34)

Manifold Absolute Pressure (MAP) Too Low

Step

Action

Value(s)

Yes

Was the "On-Board Diagnostic (OBD) System

Check" performed?

Go to Step 2

Go to OBD

System

Check

1. Ignition ON engine OFF.

2. With the throttle closed, observe the MAP value

displayed on the Scan Tool.

Is the MAP value near the specified value?

10.3 kPa

at sea level

Go to Step 4

Go to Step 3

1. Ignition ON, engine OFF.

2. Using a Scan Tool, monitor info for Diagnostic Trouble

Code 34.

Does the Scan Tool indicate Diagnostic Trouble Code 34

failed?

Go to Step 4

Refer to

Diagnostic

Aids

1. Ignition OFF.

2. Disconnect the MAP sensor electrical connector.

3. Jumper the 5 volt reference circuit and the MAP signal

together at the MAP sensor harness connector.

4. Ignition ON.

5. Observe the MAP value displayed on the Scan Tool.

Is the MAP value near the specified value?

104 kPa

Go to Step 10

Go to Step 5

1. Disconnect the jumper.

2. Connect a test light between B+ and the MAP sensor

signal circuit at the MAP sensor harness connector.

3. Observe the MAP value displayed on the Scan Tool.

Is the MAP value near the specified value?

104 kPa

Go to Step 6

Go to Step 8

DRIVEABILITY AND EMISSIONS 6E1-179

DTC (Flash DTC = 34)

Manifold Absolute Pressure (MAP) Too Low (Cont'd)

Step

Action

Value(s)

Yes

1. Ignition OFF.

2. Disconnect the ECM and check the 5 volt reference

circuit for an open or short to ground.

3. If the 5 volt reference circuit is open or shorted to

ground, repair it as necessary.

Was the 5 volt reference circuit open or shorted to

ground?

Verify repair

Go to Step 7

Check the 5 volt reference circuit for a poor connection at

the ECM and replace the terminal if necessary.

Did the terminal require replacement?

Verify repair

Go to Step 11

1. Ignition OFF.

2. Disconnect the ECM, and check the MAP signal circuit

for an open,short to ground, or short to the sensor

ground circuit.

3. If the MAP sensor signal circuit is open or shorted to

ground, repair it as necessary.

Was the MAP signal circuit open or shorted to ground?

Verify repair

Go to Step 9

Check the MAP sensor signal circuit for a poor connection

at the ECM and the MAP sensor; replace the terminal if

necessary.

Did the terminal require replacement?

Verify repair

Go to Step 11

Replace the MAP sensor.

Is the action complete?

Verify repair

Replace the EPROM or ECM.

Note) Refer to 6E1-243.

Is the action complete?

Verify repair

6E1-180 DRIVEABILITY AND EMISSIONS

Content .. 85 86 87 88 ..