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Isuzu engine C22NE / 22LE / 20LE. Manual - part 77

DRIVEABILITY AND EMISSIONS 6E1-137

0.5

RED

0.75

GRN

0.75

0.5

GRN

Engine

Control

Module

(ECM)

F14

5 Volt

Reference

Signal

Throttle

Position

(TP)

Sensor

Input

Sensor

Ground

Sensor

Ground

Throttle

Position

(TP)

Sensor

B C

Manifold

Absolute

Pressure

Sensor

Engine

Coolant

Temperature

Sensor

OUT

0.5

L/R

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 21)

THROTTLE POSITION (TP) SENSOR CIRCUIT HIGH INPUT

Circuit Description

The throttle position (TP) sensor circuit provides a

voltage signal that changes relative to throttle blade

angle. The signal voltage will vary from below 1 volt at

closed throttle to about 4 volts at wide open throttle

(WOT).

The throttle Position signal is used by the engine

control module (ECM) for fuel control and most of the

PCM-controlled outputs. If the ECM detects a low

impedance short to battery in the Throttle Position

sensor or circuit, then a code 21 will set.

Conditions for setting the DTC

• Throttle Position Sensor signal is greater than 4.69

volts.

• Engine revolution is less than 3000rpm and

manifold vacuum is less than 85kpa.

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL) the first time the fault is detected.

• The ECM will use a default throttle position based

on RPM. Conditions for Clearing the MIL/DTC

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. If the harness appears to be OK, observe

the Throttle Position sensor display on the Scan

Tool while moving connectors and wiring harnesses

related to the throttle Position sensor. A change in

the display will indicate the location of the fault.

6E1-138 DRIVEABILITY AND EMISSIONS

• Faulty Throttle Position sensor - With the ignition

key ON engine OFF observe the Throttle Position

sensor display on the Scan Tool while slowly

depressing the accelerator to wide open throttle. If a

voltage over 4.88 volts is seen at any point in

normal accelerator travel, replace the Throttle

Position sensor.

Test Description

Number(s) below refer to the step number(s) on the

Diagnostic Chart.

7. Components that share the Throttle Position

sensor 5 volt reference circuit include the following

device:

• Engine Coolant Temperature Sensor
• MAP Sensor

Disconnect the component while observing the

Throttle Position sensor display on the Scan Tool. If

the reading changes drastically when this

component is disconnected, replace the component

that affected the reading.

DTC (Flash DTC = 21)

Throttle Position (TP) Sensor Circuit High Input

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 "Throttle Position

Sensor" values displayed on the Scan Tool.

Is the "Throttle Position Sensor" above the specified

value?

4.78V

Go to Step 4

Go to Step 3

1. Ignition ON, engine OFF.

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

Code 21.

Does the Scan Tool indicate Diagnostic Trouble Code 21

failed.

Go to Step 4

Refer to

Diagnostic

Aids

1. Disconnect the Throttle Position sensor electrical

connector.

2. Observe the "Throttle Position Sensor" values

displayed on the Scan Tool.

Is the "Throttle Position Sensor" near the specified

value?

Go to Step 5

Go to Step 6

Probe the sensor ground circuit at the Throttle Position

sensor harness connector with a test light connected to

B+.

Is the test light ON?

Go to Step 7

Go to Step 10

DRIVEABILITY AND EMISSIONS 6E1-139

DTC (Flash DTC = 21)

Throttle Position (TP) Sensor Circuit High Input (Cont'd)

Step

Action

Value(s)

Yes

1. Ignition OFF disconnect the ECM.

2. Ignition ON, engine OFF.

3. Check for a short to voltage on the Throttle Position

sensor signal circuit.

4. If the Throttle Position sensor signal circuit is shorted,

repair it as necessary.

Was the Throttle Position sensor signal circuit shorted?

Verify repair

Go to Step 12

1. Ignition ON.

2. Monitor the "Throttle Position Sensor" Scan Tool

display while disconnecting each of the components

that share the 5 volt reference circuit (one at a time).

3. If the "Throttle Position Sensor" values displayed

changes, replace the component that caused the

display to change when disconnected.

Does disconnecting any of these components cause the

"Throttle Position Sensor" values displayed to change?

Verify repair

Go to Step 8

1. Ignition OFF disconnect the ECM.

2. Ignition ON, engine OFF.

3. Check for a short to B+ on the 5 volt reference circuit.

4. If the 5 volt reference circuit is shorted, repair it as

necessary.

Was the 5 volt reference circuit shorted?

Verify repair

Go to Step 9

Check for poor electrical connections at the Throttle

Position Sensor and replace terminals if necessary.

Did any terminals require replacement?

Verify repair

Go to Step 11

1. Ignition OFF.

2. Disconnect the ECM, and check for an open sensor

ground circuit to the Throttle Position Sensor.

3. If a problem is found, repair it as necessary.

Was the sensor ground circuit to the Throttle Position

Sensor open?

Verify repair

Go to Step 12

Replace the Throttle Position Sensor.

Is the action complete?

Verify repair

Replace the EPROM or ECM.

Is the action complete?

Note) Refer to 6E1-243.

Verify repair

6E1-140 DRIVEABILITY AND EMISSIONS

Content .. 75 76 77 78 ..