Reading and Writing Immobilizer EEPROMs in Circuit

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Sometimes when working with immobilizer EEPROMs, the ideal way of programming the EEPROM is by doing it while it is in the circuit, as removing it, programming and resoldering it back to the circuit, adds a bit more of effort to complete the job.

Doing it “in-circuit” can be accomplished by using the SOIC-8 clip, connecting it over the EEPROM chip while it is in circuit, but sometimes, some inconveniences are present. Some of those inconveniences are; the need of cleaning the EEPROM leads from any protecting coating the ECM might have, like silicon or soldering flux, or the fact that the EEPROM in question might have a too low profile, making it impossible to have enough grip on the chip body to keep the clip in place. Also, the situation that we will cover here; the ECM circuit is sensitive to voltages that the EEPROM programmer injects to it while reading or writing the EEPROM chip. In this case, the problem is that the micro-controller Unt (MCU) of the ECM, receives enough current from the EPROM programmer that it actually attempts to start (run). This situation will vary from ECM to ECM and from programmer to programmer, but to be in the safe side, we have a simple solution here.

The solution for this situation is to disable the crystal oscillator of the MCU that is attempting to run with the programmer’s voltage. That is accomplished by simply jumping the crystal by running either a 0.1uf capacitor or a small jumper wire across it. In the picture below, it is shown how a 0.1uf capacitor was temporarily soldered across the crystal terminals to disable it.

In the event that you don’t have an SOIC-8 SMD clip to read and write the immobilizer EEPROM or simply you don’t like it, below is pictured another approach for doing it. For this, you will need to construct the harness, composed of 8 micro clips and a 4-pin dual header for connecting it to the programmer. Once constructed, you will be able to use it over and over. It will have even more life span than the SOIC clip itself. If you decide to construct it yourself, be as neat as possible and use high quality materials so you end up making a durable tool and don’t just make a prototype like the one shown here 🙂

There are Internet stores that sell some of the equipment used on this job. For example, you may get the SOIC-8 SMD clip complete with its harness and ready to use from stores over the Internet. You will find examples below.

On a final note, please be always careful when working with static sensitive electronic circuits and devices. Always use an ESD (Electro Static Discharge) protection to avoid unrepairable damage to the circuits and/or devices.

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