Certain OBD1 ECUs, such as the P05 and JDM P08, lack the internal circuitry required to drive a 4-wire heated O2 sensor. Failure to enable this circuit will result in a diagnostic trouble code (DTC). The following modifications allow for the integration of the O2 heater control.

P05 ECU Modification#

To enable O2 heater functionality on a P05 ECU, you must populate the missing transistor circuit.

• Component: Transistor Q30
• Part Number: C144 (or equivalent NPN switching transistor)

JDM P08 ECU Modification#

JDM ECUs lacking heater circuitry require an SMT transistor to be installed on the underside of the PCB.

• Component: Transistor Q15
• Part Number: MMBT4401 (SMT version of the 2N4401 general-purpose NPN switching transistor)

Important

Ensure the transistor is oriented correctly according to the PCB silkscreen markings. Improper orientation or soldering may result in damage to the ECU's driver circuit.

Tip

These components are standard electronic parts and can be sourced through major electronics distributors such as Digi-Key or Mouser.