When the car won’t start, we need to use diagnose tool or scanner to read the code to find what the fault is, then analyze the possible causes and use differential diagnosis method to find the exact cause. In this post we will share the procedure we fix the Honda Jazz won’t start.

Vehicle information

Model: Honda Jazz

Year: 2015


Fault symptom

The car won’t start after pressing the gas pedal.


Diagnose process

  1. Connect HDS with car, got 4 fault codes, code P0122, P0222 and P2127 all is sensor voltage too low. The possible causes: The sensor fault signal line is short-circuited or disconnected, or the power line is faulty. The three sensors do not share the signal line, so the probability of the signal line being short-circuited or disconnected at the same time is very small, plus the fault code P0651, so the most likely point of failure is the power line.
  2. Find the circuit diagram, refer to the vehicle wiring diagram and the PCM pin definition. The reference voltage of TP sensor A / B is VCC3, and the reference voltage of APP sensor A / B is VCC4 and VCC5.
  3. How the reference voltage is generated: When the ignition switch is turned to the second gear, IG1 (C10) powers the PCM, the PCM starts to work and then the PCM command pin A7 (control line) is turned on, the main relay 1 works, and IGP (A9) Electricity, the entire PCM starts to work. Inside the PCM, the standard 5V voltage is converted by a transformer, and power is supplied to VCC1, VCC2, VCC3 ..., the reference voltage.
  4. VCC1, VCC2, VCC3 ... These 5V power lines are connected within the PCM and provide power to each sensor.
  5. Measure any one of the voltage lines VCC1, 2, and 3 on the PCM. If the voltage is found to be too low (normal 5v), we know that these pins are connected inside the PCM. We can be sure that there is a short circuit in these power lines causing the entire system to be without electricity. Then we unplug the sensors connected to these power cords one by one, and we can find the problem.
  6. Based on the above analysis, first retrieve the comprehensive troubleshooting in the maintenance manual according to fault code P0651
  7. When the 3-pin connector of the air-conditioning pressure sensor is disconnected, the fault disappears and the fault point is locked, which is due to the power system failure caused by short-circuit of the air-conditioning pressure sensor.
  8. Replace the air-conditioner pressure sensor and the fault disappear.


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