With the laptop online and the engine not running, go through these checks one at a time. Each takes seconds, and a wrong reading now is far easier to trace than a no-start later.
- Throttle position. Press the pedal slowly to the floor and let it back. The TPS reading should follow smoothly with no jumps or dropouts. If it hasn't been calibrated yet, do it now.
- MAP sensor. Key on, engine off, the manifold is at atmospheric pressure, so the MAP reading should be close to it: roughly 14.7 psi (101 kPa) at sea level, a little lower at altitude.
- Coolant temperature. Should match what you'd expect. A cold engine reads close to the air temperature in the shop.
- Air temperature. Should also be close to the ambient temperature.
- Fuel pump prime. Listen for the pump running briefly when the ECU powers up.
| Reading | Usually |
|---|---|
| TPS doesn't move | Signal on the wrong input, or no 5V supply |
| MAP far from atmospheric | Wrong sensor calibration selected, or wiring error |
| Temps read extreme values | Open or shorted sensor circuit, or wrong calibration |
| No pump prime | Relay, fuse or fuel pump output setup |
Before this step, confirm power, ground and communications. After it, move on to checking crank and cam sensors and calibrating ignition timing.
