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 micro-controller 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.


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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 🙂


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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.

What other users are looking for:

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  • Calvin says:

    When i open my car speedometer i didnt see 93c56 chip, i can only see a chip with c56 d910 writing on it
    If you interested in this car chip i can send you the picture
    Please tell me how do i read and write data to this chip

  • Calvin says:

    I cant.clip using the pomona clip
    Because the chip too small
    8pin chip but smaller.than the pomona.clip
    Please help how to program this chip

  • zilog357 says:

    Hello Calvin. When that happens, the solutions are two; take out the chip (desolder) and grab it with the clip, or use 8 wires with micro-pincers at one end and a DIL-9 terminal at the other. The solution is here in the blog, but looks like images are not showing for some reason after an update of the software. We are working to have the website back to normal, so you may visit us at a later time to see if the contents is restored.

  • J haro says:

    Hello I have one question what is safer reding and writing the EEPROM un circuit or resoldering the chip thanks.

  • zilog357 says:

    Hello Josue. Obviously it is safer to desolder the EEPROM, but the in-circuit approach is tried first as a way of saving time and sometimes, saving the circuit if you don’t have the needed tools to work with surface-mount devices. Depending on the ECM circuit -AND- on the device programmer, you will be able to do it in circuit in some models, but there will be others that no matter what you try, the EEPROM will need to be out of circuit to be read correctly.

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