Reading and Writing Immobilizer EEPROMs in Circuit
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, add a bit more of effort to complete the job.
Doing it “in-circuit” can be accomplished in many ECMs (not all) by using the SOIC-8 clip, connecting it over the EEPROM chip while it is in the 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 latter case, the problem is that the microcontroller unit (MCU) of the ECM, receives enough current from the EPROM programmer that it actually attempts to startup(run). This situation will vary from ECM to ECM and from programmer to programmer, but if it tries to start up, the data being sent from the programmer to the EEPROM gets corrupted. To be on the safe side, we have a simple solution here.
The solution for this situation is to disable the crystal oscillator of the MCU in the ECM circuit to prevent it from running. That is accomplished by simply jumping the crystal by running either a 0.1uf capacitor or a small jumper wire across it (in parallel with the crystal oscillator). 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 a SOIC-8 SMD clip to read and write the immobilizer EEPROM or you simply don’t like that method for being somewhat unreliable, below is pictured another approach for doing it. For this, you will need to construct the harness or buy it already assembled, as it is already available to be ordered online. It is made of 8 micro clips and an 8 connections dual pin header (4 + 4) for connecting it to the programmer. Once constructed, you will be able to use it over and over. It will have even more of a lifespan 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 online 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 electronics. Always use an ESD (Electro Static Discharge) protection to avoid unrepairable damage to the circuits and/or devices.
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