Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
With "SCAN" Tester
A "SCAN" tester provides a visual reading of most of the ECM inputs and some of the outputs controlled by the ECM. With the "SCAN" tester in the code position, the stored code will be displayed in the display window.
By connecting the "SCAN" tester to the ALDL connector and a 12-volt power supply, valuable information can be received from the CCC system. The technician's knowledge of the system and understanding of the "SCAN" tester's limitations can provide information that would otherwise be difficult to obtain. However, "SCAN" testers cannot replace volt/ohmmeters when called for within diagnostic charts.
The "SCAN" tester can display the following information in the display window:
- "ON" when ECM has commanded A/C clutch into operation. This does not mean that A/C clutch is operating, only that ECM has instructed it to commence operation.
- "YES" when A/C is activated.
- Actual battery voltage reading detected at ECM ignition input.
- "CLOSED LOOP" or "OPEN LOOP", depending upon mode that engine control system is operating under.
- Diagnostic codes.
- Coolant temperature in degrees Centigrade.
- RPM that ECM is trying to maintain at idle.
- "ON" when ECM has commanded EGR valve to open. This does not mean that EGR valve is open, only that ECM has instructed EGR valve to open to allow EGR flow.
- Position of EGR valve pintle.
- "YES" when transmission is in fourth gear.
- A number that represents the position that the ECM thinks the idle air control valve is in at that time.
- A number, in milliseconds, that represents the pulse width ("on" time) that the ECM is commanding to the injectors.
- Amount of spark retard in number of degrees.
- "YES" when knock is detected or "NO" when knock is not detected.
- Manifold air temperature in degrees Centigrade.
- Low voltage when the manifold pressure is low (high vacuum), or high voltage when the pressure is high (low vacuum).
- Vehicle speed in miles per hour.
- Oxygen sensor reading ranging from 1 to 999 millivolts. If consistently below 350 millivolts, fuel system is lean; if consistently above 550 millivolts, fuel system is rich.
- Percent of throttle angle.
These are only some of the capabilities of the "SCAN" tester. Consult "SCAN" tester manufacturer's diagnostic manual for complete explanation of the tester and its limitations.
| Code | Circuit Affected |
|---|---|
| 13 | Open Oxygen Sensor Circuit |
| 14 | Coolant Sensor Signal Voltage High |
| 15 | Coolant Sensor Signal Voltage Low |
| 21 | TPS Signal Voltage High |
| 22 | TPS Signal Voltage Low |
| 23 | MAT Sensor Signal Low (2.5L Only) |
| 24 | Vehicle Speed Sensor Circuit |
| 25 | MAT Sensor Signal High (2.5L Only) |
| 32 | EGR System Failure |
| 33 | MAP Sensor Signal Voltage High |
| 34 | MAP Sensor Signal Voltage Low |
| 35 | Idle Speed Error (2.5L Only) |
| 42 | EST Circuit |
| 43 | ESC Circuit (Except 2.5L & 7.4L) |
| 44 | Lean Exhaust Indication |
| 45 | Rich Exhaust Indication |
| 51 | Faulty MEM-CAL (2.5L), PROM, or ECM |
| 52 | Fuel CALPAK Missing (Except 2.5L) |
| 53 | Charging System Voltage High |
| 54 | Fuel Pump Circuit Low Voltage |
| 55 | Replace ECM |
NO RELATED
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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.