ECM Data: Notes
You can retrieve data from the ECM by connecting a scan tool or the HDS to the data link connector (DLC). The items listed in the table below conform to SAE recommended practice. The HDS also reads data beyond that recommended by SAE to help you find the causes of intermittent problems.
NOTE:
The "operating values" listed are approximate and may vary depending on the environment and the individual vehicle. Unless noted otherwise, "at idle speed" means idling with the engine completely warmed up, in neutral position, and the A/C and all accessories turned off.
DATA DESCRIPTION CHART
| Data | Description | Operating Value | Freeze Data |
|---|---|---|---|
| Diagnostic Trouble Code (DTC) | If the ECM detects a problem, it will store it as a code consisting of one letter and four numbers. Depending on the problem, an SAE-defined code (P0xxx, P2xxx) or a Honda-defined code (P1xxx) will be output to a scan tool or the HDS. | If no problem is detected, there is no output. | YES |
| Engine Speed | The ECM computes engine speed from the signals sent from the Crankshaft Position (CKP) sensor. This data is used for determining the time and amount of injected fuel. | Nearly the same as tachometer indication At idle speed: 800+/-50 RPM | YES |
| Vehicle Speed | The ECM converts pulse signals from the Vehicle Speed Sensor (VSS) into speed data. | Nearly the same as speedometer indication | YES |
| Manifold Absolute Pressure (MAP) | The absolute pressure caused in the intake manifold by engine load and speed. | With engine stopped: Nearly the same as atmospheric pressure At idle speed: 28-48 kPa (8.3-14.2 in.Hg, 210-360 mmHg) | YES |
| Engine Coolant Temperature (ECT) | The ECT sensor converts coolant temperature into voltage, and sends a voltage signal to the ECM. The sensor is a thermistor whose internal resistance changes with coolant temperature. The ECM uses the voltage signals from the ECT sensor to determine the amount of injected fuel. | With cold engine: Same as ambient temperature and IAT With engine warmed up: about 176-212 °F (80-100 °C) | YES |
| Primary Heated Oxygen Sensor (Primary HO2S) (Sensor 1), Secondary Heated Oxygen Sensor (Secondary HO2S) (Sensor 2) | The HO2S detects the oxygen content in the exhaust gas and sends voltage signals to the ECM. Based on these signals, the ECM controls the air/fuel ratio. When the oxygen content is high (that is, when the ratio is leaner than the stoichiometric ratio), the voltage signal is lower. When the oxygen content is low (that is, when the ratio is richer than the stoichiometric ratio), the voltage signal is higher. | 0.0-1.4V At idle speed: about 0.1-0.9 V | NO |
| Fuel System Status | Fuel system status is indicated as "open" or "closed". Closed: Based on the HO2S output, the ECM determines the air/fuel ratio and controls the amount of injected fuel. Open: Ignoring HO2S output, the ECM refers to signals from the throttle position (TP), manifold absolute pressure (MAP), intake air temperature (IAT), barometric pressure (BARO) and engine coolant temperature (ECT) sensors to control the amount of injected fuel. |
At idle speed: closed | YES |
| Short Term Fuel Trim | The air fuel ratio correction coefficient for correcting the amount of injected fuel when the Fuel System Status is "closed". When the ratio is leaner than the stoichiometric ratio, the ECM increase short term fuel trim gradually, and the amount of injected fuel increases. The air fuel ratio gradually gets richer, causing a lower oxygen content in the exhaust gas. Consequently, the short term fuel trim is lowered, and the ECM reduces the amount of injected fuel. This cycle keeps the air/fuel ratio close to the stoichiometric ratio when in closed loop status. | 0.73-1.47 | YES |
| Long Term Fuel Trim | Long term fuel trim is computed from short term fuel trim and indicates changes occurring in the fuel supply system over a long period. If long term fuel trim is higher than 1.00, the amount of injected fuel must be increased. If it is lower than 1.00, the amount of injected fuel must be reduced. | 0.80-1.20 | YES |
| Intake Air Temperature (IAT) | The IAT sensor converts intake air temperature into voltage and signals the ECM. When intake air temperature is low, the internal resistance of the sensor increases, and the voltage signal is higher. | With cold engine: Same as ambient temperature and ECT | YES |
| Throttle Position | Based on the accelerator pedal position, the opening angle of the throttle valve is indicated. | At idle speed: about 6 % | YES |
| Ignition Timing | Ignition timing is the ignition advance angle set by the ECM. The ECM matches ignition timing to the driving conditions. | At idle speed: 5°+/-5°BTDC with the SCS service signal line jumped with the HDS | NO |
| Calculated Load Value (CLV) | CLV is the engine load calculated from the MAP data. | At idle speed: 22-42 % At 2,500 RPM without load: 27-48 % | YES |