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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, or the fact that the EEPROM in question might have a too low profile, making it impossible to keep the clip in place, or the situation that we will cover here; the ECM circuit is too sensitive to the voltage that the EEPROM programmer injects to it, for working (reading/writing) with the EEPROM. In this case, the problem is that the micro controller of the ECM is attempting to start (run) with the reading supplied voltage. Of course, thus will vary from ECM to ECM and from programmer to programmer.

The solution for this situation is to disable the crystal oscillator of the micro controller (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.

Disabling a Crystal Oscillator for reading EEPROM

In the event that you don’t have the SOIC 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.

Using the Spider to read in-circuit EEPROMs
Using the Spider on SMD EEPROMs

There are some Internet stores that sell some of the equipment used on the described jobs. For example, you may get the SOIC-8 SMD clip complete with its harness and ready to use from MCMall. For the link, just click on the picture below:

SOIC-8 SMD clip complete with harness

The microclips can be obtained from the electronics distributors, DigiKey. The link is below along with the picture.

SMD Micro Pincers from Digikey

Good luck and be always careful when working with sensitive electronic circuits by using ESD (ElectroStatic Discharge) protection to avoid damaging the circuits.

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