Isuzu engine C22NE / 22LE / 20LE. Service manual — part 77
DRIVEABILITY AND EMISSIONS 6E1-137
0.5
R
0.5
G
0.5
GR
0.5
RED
0.75
GRN
0.75
L
0.5
GRN
Engine
Control
Module
(ECM)
F14
B1
A3
5 Volt
Reference
Signal
Throttle
Position
(TP)
Sensor
Input
Sensor
Ground
Sensor
Ground
B7
B2
Throttle
Position
(TP)
Sensor
B C
A
Manifold
Absolute
Pressure
Sensor
Engine
Coolant
Temperature
Sensor
B8
LO
HI
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
No
1
Was the "On-Board Diagnostic (OBD) System Check"
performed?
-
Go to Step 2
Go to OBD
System
Check
2
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
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
4
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?
0V
Go to Step 5
Go to Step 6
5
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
No
6
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
7
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
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
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
10
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
11
Replace the Throttle Position Sensor.
Is the action complete?
-
Verify repair
-
12
Replace the EPROM or ECM.
Is the action complete?
Note) Refer to 6E1-243.
-
Verify repair
-
6E1-140 DRIVEABILITY AND EMISSIONS
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