Diagnostic Circuit Check

SCAN DATA

Scan Position

⁽¹⁾ Data Value

A/C

No (Yes W/ A/C Requested)

A/C Clutch

Off (On W/ A/C Requested)

Air Control Solenoid

Off

Air Fuel Ratio

0-25.5:1

Battery

13-15 Volts

BARO-

Voltage Varies Depending On Altitude

BLE (Block Learn Enable)

Yes

BLM (Block Learn Memory)

116-145 Counts

Block Learn Cell

BPW (Base Pulse Width)

0-499.9 Milliseconds

Canister Purge

Off

Coolant Temperature

185-221°F (85-105°C)

EGR Solenoid

Off

EST (Electronic Spark Timing)

Yes

IAC (Idle Air Control)

1-50 Counts

Idle Throttle

Yes

INT (Integrator)

Varied 108-154 Counts

Knock Retard

0-45 Degrees

MAP (Manifold Absolute Pressure)

⁽²⁾ 1-2 Volts

MAT (Manifold Air Temperature)

⁽³⁾ 50-199°F (10-93°C)

Open/Closed Loop

Closed Loop

Oxygen Sensor

⁽³⁾ .1-1.0 Volt

PARK/NEUTRAL Position

Park/Neutral

Power Steering Switch

Normal

Prom Identification

0-65535

RPM

⁽⁴⁾⁽⁵⁾ RPM Is Controlled By ECM

Rich/Lean Flag

Varies

Second Throttle Solenoid

Off (On Above 5000 RPM)

Shift Light

Off

Spark Advance

Varies

Throttle Angle

Zero Percent At Idle

TPS (Throttle Position Sensor)

.50-.1.25 Volts

VSS (Vehicle Speed Sensor)

0 MPH

⁽¹⁾	With engine idling at normal operating temperature, in Park or Neutral, system in closed loop and all accessories off.

⁽²⁾	Voltage varies with vacuum and barometric pressure.

⁽³⁾	Voltage varies with exhaust temperature.

⁽⁴⁾	Plus or minus 50 RPM from desired RPM (A/T).

⁽⁵⁾	Plus or minus 100 RPM from desired RPM (M/T).

Diagnostic circuit check will identify problem created by Electronic Engine Control System (EECS) malfunction. It is the starting point for diagnosis. This check will direct you to the next logical step in diagnosing the complaint.

After completing diagnostic circuit check and finding on-board diagnostics functioning properly with no trouble codes displayed, use appropriate SCAN DATA table for comparison.

Data values must be taken under these conditions:

Engine at normal operating temperature.
Engine running at idle.
Vehicle in Park or Neutral.
System in closed loop.

NOTE: The values are an average of displayed values recorded from normal operating vehicles. Values represent what a normal functioning system would typically display.

NOTE: Only parameters supplied by manufacturer are used in this article. If a scan tester reads other parameters, values are not recommended by manufacturer for diagnostic use. A scan tester displaying faulty data should not be used, or misdiagnosis will occur. Report problem to scan tester manufacturer.

NOTE: Test numbers refer to numbers on diagnostic chart.

This step checks if ECM can provide a ground path for CHECK ENGINE light. This is a bulb check.
This step checks if ECM can perform internal diagnostics.
This step checks if ECM can supply serial data for scan tester.
This step verifies scan data.
This step checks whether ECM or electrical system is cause of no start.
This step checks ECM memory for codes to aid in diagnosis.

Fig 1: Diagnostic Circuit Check

Courtesy of ISUZU MOTOR CO.