Recently, a reader (James) sent me an email asking what he must do to return his P28 ECM to stock specifications after a performance chip was installed. I tried to reply in two occasions, but both emails bounced probably because of a wrong email address entered when sending the contact form, so this is an attempt to answer the question in hope he will read it. Although he have a P28-L01 (Californian – Manual ECM), this applies to all P28, with the exception of Japanese market P28’s.

Before answering this, let me explain that the P28 ecm is not like ecms that you just replace the stock chip for a performance one. In case of a P28, the ecm is running with the stock program which is embedded inside the microcontroller itself. When a performance chip is installed, it is added, but not replaced by a stock part. Besides adding the chip, several other electronic components must be added so the ecm can “realize” that chip is installed and read it. Those other components are two capacitors, a resistor, the performance chip, a small electronic latch chip and the key between performance (new chip) and stock specs (internal program), a jumper (”J1″).

Well for answering the question, just leave the performance parts in circuit and just cut or disconnect the jumper “J1″. When jumper J1 is connected, the ecm will read the new installed chip (performance), but when J1 is cut, the ecm will read its internal program again and all other parts will be transparent for it.

Good Luck.

Best regards,

Richard

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