The OBD1 ECU processes Throttle Position Sensor (TPS) data using an 8-bit integer value. This reference provides the formula for converting raw hexadecimal ECU data into a percentage of throttle opening.

Conversion Formula#

To calculate the throttle percentage from an 8-bit TPS value ($x$), use the following formula:

$$\text{TPS}(x) = \left( \frac{\text{hex_to_dec}(x)}{229.5} \right) \times 100%$$

Wide Open Throttle (WOT) Calibration#

The ECU defines Wide Open Throttle (100%) based on a voltage threshold of 4.5V. The 8-bit scaling is derived as follows:

• WOT Voltage: 4.5V
• Reference Voltage: 5.0V
• Calculation: $(4.5 / 5.0) \times 255 = 229.5$

Note

The value 229.5 represents the raw 8-bit integer value corresponding to 100% throttle opening. Values exceeding this threshold are typically clamped by the ECU firmware.