ECM/PCM Data
By connecting the OBD II scan tool or the Honda PGM Tester to the 16P data link connector (DLC), various data can be retrieved from the ECM/PCM. The items listed in the table below conform to the SAE recommended practice.
The Honda PGM Tester also reads data beyond that recommended by SAE.
Understanding this data will help to find the causes of intermittent failures or engine problems.
NOTE:
- The "operating values" given below are approximate values and may be different depending on the environment and the individual vehicle.
- Unless noted otherwise, "at idle speed" means idling with the engine completely warmed up, A/T in position [P] or [N], M/T in neutral, and the A/C and all accessories turned off.
DATA DESCRIPTION
| Data | Description | Operating Value | Freeze Data |
|---|---|---|---|
| Diagnostic Trouble Code (DTC) | If the ECM/PCM 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) or a Honda-defined code (P1xxx) will be output to the tester. | If no problem is detected, there is no output. | ◦ |
| Engine Speed | The ECM/PCM computes engine speed from the signals sent from the Crankshaft Position sensor. This data is used for determining the time and amount of fuel injection. |
Nearly the same as tachometer indication. | ◦ |
| Vehicle Speed | The ECM/PCM converts pulse signals from the Vehicle Speed Sensor (VSS) into speed data. | Nearly the same as speedometer indication | ◦ |
| 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: 24-37 kPa (180-280 mmHg, 7.1 - 11.0 inHg) | ◦ |
| Engine Coolant Temperature (ECT) | The ECT sensor converts coolant temperature into voltage and signals the ECM/PCM. The sensor is a thermistor whose internal resistance changes with coolant temperature. The ECM/PCM uses the voltage signals from the ECT sensor to determine the amount of injected fuel. | With cold engine: Same as ambient temperature and I AT With engine warmed up: 176-194°F (80-90°C) | ◦ |
| Heated Oxygen Sensor (HO2S) (Primary, Sensor 1) (Secondary Sensor 2) | The Heated Oxygen Sensor detects the oxygen content in the exhaust gas and sends voltage signals to the ECM/PCM. Based on these signals, the ECM/PCM 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. |
0.0-1.25 V At idle speed: about 0.1 - 0.9 V | X (Sensor 1) |
| HO2S Feedback Loop Status | Loop status is indicated as "open" or "closed". Closed: Based on the HO2S output, the ECM/PCM determines the air/fuel ratio and controls the amount of injected fuel. Open: Ignoring HO2S output, the ECM/PCM refers to signals from the TP, MAP, and ECT sensors to control the amount of injected fuel. |
At idle speed: closed | ◦ |
| Short Term Fuel Trim | The air/fuel ratio correction coefficient for correcting the amount of injected fuel when HO2S feedback is in the closed loop status. When the signal from the HO2S is weak, short term fuel trim gets higher, and the ECM/PCM increases the amount of injected fuel. The air/fuel ratio gradually gets richer, causing a higher HO2S output. Consequently, the short term fuel trim is lowered, and the ECM/PCM reduces the amount of injected fuel. This cycle keeps the air/fuel ratio close to the stoichio-metric ratio when in closed loop status. | ±20% | ◦ |
| 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. |
± 20% | ◦ |
| Intake Air Temperature (IAT) | The IAT sensor converts intake air temperature into voltage and signals the ECM/PCM. 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 | ◦ |
| Throttle Position | Based on the accelerator pedal position, the opening angle of the throttle valve is indicated. | At idle speed: approx. 10% | ◦ |
| Ignition Timing | Ignition timing is the ignition advance angle set by the ECM/PCM. The ECM/PCM matches ignition timing to the driving conditions. | At idle speed: 12° ± 2° BTDC with the SCS service connector connected. | x |
| Calculated Load Value (CLV) | CLV is the engine load calculated from the MAP data. | At idle speed: 15-35% At 2,500 rpm with no load: 12-30% |
◦ |