The diagnostic circuit check will identify a problem created by an Electronic Engine Control System (EECS) malfunction. It is the starting point for diagnosis. This directs you to the next logical step in diagnosing a 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. The typical values are an average of display values recorded from a properly operating vehicle and are intended to represent a normal system 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 a misdiagnosis will occur. Report problem to scan tester manufacturer.

SCAN DATA

Scan Position

⁽¹⁾ Data Value

A/C Clutch

Off

A/C Request

Base Pulse Width (BPW)

.8-3.0 Milliseconds

Battery

13.5-14.5 Volts

Block Learn Cell

Block Learn Enable

Block Learn Memory (BLM)

118-138 Counts

Coolant Temperature

185-221°F (85-105°C)

Desired RPM

ECM Idle Command

EGR Solenoid

Off

EGR Temp. Signal

0-5 Volts

Engine RPM

DOHC

Non-Turbo

800-900 RPM

Turbo

800-1000 RPM

SOHC

A/T

890-990 RPM

M/T

800-900 RPM

IAC

1-50 Counts

Idle Throttle

Integrator (INT)

110-145 Counts

MAP

⁽²⁾ .5-2.0 Volts

MAT Temperature

⁽³⁾ 50-194°F (10-90°C)

Open/Closed Loop

Closed Loop (Open w/Extended Idle)

Oxygen Sensor

⁽⁴⁾ .1-1.0 Millivolts

Park/Neutral Switch

Park/Neutral

Power Steering Switch

Normal

Shift Light (M/T)

Off

Spark Advance

Varies

Throttle Angle (%)

TPS

.4-1.25 Volts

Vehicle Speed

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

⁽²⁾	Depending on vacuum and barometric pressure.

⁽³⁾	Depending on underhood temperature.

⁽⁴⁾	Voltage will continuously vary.

Fig 1: Diagnostic Circuit Check Flow Chart

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Diagnostic Circuit Check

Use the Manual With the Right Hardware

When to See a Mechanic