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 effort and time to complete the job.
Doing it “in-circuit” can be accomplished in many ECMs (not all) by using the SOIC-8 clip or 8 separate SMD pincers and connecting any of those two solutions 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 silicon, glue, or resin/flux coating the ECM might have in the circuit covering the individual components. Another problem (for the clip) is if the EEPROM in question has a too low profile, making it impossible to have enough grip on the chip body to keep the clip in place.
Possible problems of using this appoach
Above all inconveniences of programming an EEPROM in an “in-circuit” fashion is the possible situation that the microcontroller (MCU) in the ECM circuit could be sensitive to voltages that the EEPROM programmer uses for reading and writing the EEPROM chip. This happens very often because working voltages of the MCU jumped from 5 volts to 3.3 volts and nowadays, to as low as 1.8 volts. In these cases, the problem is that the microcontroller receives enough current from the EPROM programmer that it actually attempts to start (run) its internal program. This situation will vary from ECM to ECM and from programmer to programmer, but when it happens, it will interfere with the data we are working with and will corrupt it. When this happens we will end up with an incorrect image of the EEPROM if we are in the reading process or will program the wrong data to the EEPROM if we are writing to it.
For this, we can try the common solution of disabling the crystal oscillator of the MCU to prevent it from running, or at least attempt to prevent it, as this does not work in all cases. It is accomplished by simply jumping the crystal oscillator by running either a relatively large capacitor, in this example a 0.1uf capacitor, or a small jumper wire across the crystal (in parallel to 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 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.
The mentioned wires are 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 and will even have a larger 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 for 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, on eBay for example.
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, especially if you live in cold-dry weather.
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