2003 Honda Civic 2.0L no start immobilizer

My immobilizer light came on and it used to stall and start a few days ago but now my car won't start at all. I scanned it and does not want to communicate with my scanner. It's good it happened near my house and I am now worried how much I would pay for repairs and towing. Nearest dealer is about 50 miles away. Lots of shops around my area and I wonder if this something easy that a local garage or myself can repair?

ATS Adviser:

If you can get a couple of wiring diagrams near you and have a handy digital voltmeter, maybe I can help you. The reason this might look easy because of the symptom " no communication". Just looking at the computer bus data line wiring diagram right now I can see that the immobilizer module bus wire can be accessed from your DLC pin terminal pin 6 shown as a gray wire.

However, the smart way to check the immobilizer without going to the dealer is to check the voltage of the DLC pin 15 which is the Kline bus wire. This wire connects to both em and abs modulator control unit. If you can disconnect the 2 modules one by one while watching the Kline voltage (should be around 5-7 volts depending on the engine model).

Practical way is if you unplug the ecm first then your scanner works, it is the ecm circuit problem and the same if you disconnect the abs modulator control unit. This is how I see it on the computer data bus diagram. Once both modules checked OK, then by elimination, the problem is the immobilizer control unit.

However, sice this security system would need a programming by the dealer, I would let them do it and this job takes about an hour to do. Hence no need to buy expensive programming tool.

A few guys in ATS were successful in testing the immobilizer by checking the ecm module circuit alone. They do it by by measuring the power, ground and vref supplies of the ecm pin connections.

Check this approximate bus wiring diagram from ATS below for this car. Do this 5 minute test before doing anything like mechanical repairs. When testing the DLC terminals, measure voltage at K-Line pin 15 and make sure you have 5 to 7 volts. If not, the wiring circuit is defective. Note the ground reading at pin 12 and power at pin 8.

2003 Honda Civic Bus Wires

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