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HondaPlatinum, A Technician
Category: Honda
Satisfied Customers: 11334
Experience:  13 year honda platinum level
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Immobilizer intermittently works and then doesn't. car

Customer Question

immobilizer intermittently works and then doesn't. car starts sometimes and then sometimes not
JA: Have you checked the battery, particularly the terminal connections? Are they corroded?
Customer: Clean, good connections
JA: What is the model/year of your Honda?
Customer: 2000 accord ex 2.3
JA: Are you fixing your Accord yourself? What have you tried so far?
Customer: All fuses good. the key light will flash 1x and it will start then the key light will continue to flash and it won't start. changed immobilizer at key.
JA: Anything else you want the mechanic to know before I connect you?
Customer: no
Submitted: 11 months ago.
Category: Honda
Expert:  Chad Farhat replied 11 months ago.

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

Expert:  Chad Farhat replied 11 months ago.

hey how are you

1- You need to have it scanned with a honda scanner and retrieve fault codes from anti theft module , it could any of these parts in the system, i sent you diagrams to shown all the parts involved ,but if no scanner available , look at the diagram # 3 and check the hood switch and drive door switch ,these are the common switches that go bad , especially hood switch .but testing is needed on all if no scanner available .

This is the system description

System Description

The vehicle is equipped with an immobilizer system that will disable the vehicle unless the proper ignition key is used. This system consists of a transponder located in the ignition key, an immobilizer receiver unit, an indicator light, and the ECM/PCM. The vehicle has two kinds of keys. - The black master key for: - ignition switch. - door locks. - trunk lock. - glove box. - trunk handle. - rear seat and pass through. - The gray valet key for: - ignition switch. - door locks. When the key is inserted in the ignition and turned to the (II) position, the immobilizer unit sends power to the transponder in the ignition key. The transponder then sends a coded signal back through the immobilizer unit to the ECM/PCM. - The immobilizer system can store up to six key codes. - If it is necessary to rewrite the ECM/PCM to learn a new key, the dealer needs the customer's vehicle, all its master keys and valet keys, and the Honda PGM Tester equipped with an immobilizer program card. Any key that is not learned during rewriting will no longer start the engine. - If the customer has lost his key, and cannot start the engine, contact Honda Customer Relations. - If the proper key has been used, the ECM/PCM will energize the fuel supply system. The immobilizer indicator light in the gauge assembly will simultaneously come on for about 2 seconds, then go off, indicating that the immobilizer unit has recognized the code sent by the transponder. - If the wrong key has been used and the code was not received or recognized by the ECM/PCM, the indicator light will come on for about 2 seconds, then it will continue blinking until the ignition switch is turned OFF. - If the ignition switch is turned OFF, the indicator will blink for about 5 seconds to signal that the ECM/PCM has been set correctly, then the indicator will go off.

Please let me know

Thank You

Chad Farhat

ASE Certified Technician

Expert:  Chad Farhat replied 11 months ago.

Immobilizer System How the Circuit Works The immobilizer system is designed to prevent the car from being started without the owner's ignition key. It an attempt is made to start the car with any other key, the immobilizer system will disable the car's fuel supply. The immobilizer system consists of the ignition key, immobilizer receiver unit, immobilizer indicator light, PGM-FI main relay, fuel pump, and the PCM or ECM. With the ignition switch in ON (II) or START (III), the immobilizer receiver unit and the PCM or ECM receive an ignition on" signal through fuse 46 and the PGM-FI main relay. The PCM or ECM then sends power to the ignition key transponder through the immobilizer receiver unit. The transponder then sends a coded signal back to the PCM or ECM through the receiver. If the signal is correct, the PCM or ECM will enable the car's fuel supply system by grounding the PGM-FI main relay. The immobilizer indicator light flashes a code to indicate that the correct key has been inserted. If the ignition key signal is not correct, the PCM or ECM will not enable the car's fuel supply system by not grounding the PGM-FI main relay. The immobilizer indicator light then flashes a code to indicate that an incorrect key has been inserted.

System Description Security Alarm System The security alarm system is armed automatically after the doors, hood, and trunk lid are closed and locked. For the system to arm, the ignition switch must be off, the key must be removed, and the security control unit must receive signals that the doors, hood, and trunk lid are closed and locked. The alarm can be disarmed at any time by unlocking either door with the key or the remote transmitter. When everything is closed and locked, the only control unit inputs that are grounded, and have 0 volts, are the driver's door lock knob switch, and the audio unit. In other words, all of the other switches are open, including the key cylinder switches, and they have about 10 volts. Ten seconds after the doors are locked with the key or the lock knob (with the door open), or immediately after the doors are locked with the LOCK button on the remote transmitter, the security system arms, and the security indicator on the door panel flashes. If the security indicator does not flash, the system is not arming. Check the doors, hood, and trunk to see if they are closed. A beep to confirm the security alarm system is armed will sound if the LOCK button is pressed a second time within 5 seconds. If one of the switches is misadjusted or there is a short in the system, the system will not arm. As long as the control unit continues to receive a ground signal, it senses that the vehicle is not closed and locked, and the system will not arm. Conversely, a switch that is slightly misadjusted can sound an alarm for no apparent reason. In this case, a significant change in outside temperature, the vibration of a passing truck, or someone bumping into the vehicle could cause the alarm to sound. If anything is opened or improperly unlocked after the system is armed, the control unit receives a ground signal from that switch, and the 10 volts reference drops to 0 volts. If the radio is disconnected, the input loses its ground, and the input voltage goes to 10 volts. The system sounds the alarm when any of these things occur: - A door is forced open - A door is unlocked without using the key or the remote transmitter - The hood is opened - The trunk is opened without using the transmitter - The audio unit is disconnected - The panic mode is activated When the system sounds the alarm, the security horn sounds and the exterior lights flash for 2 minutes. The alarm can be stopped at any time by unlocking either door with the key or by pushing any button on the remote transmitter. Panic Mode The panic mode allows the security system to sound the alarm with the remote transmitter in order to attract attention. When the PANIC button is pressed and held for 2 seconds, the alarm will sound and the exterior lights will flash for about 30 seconds. The panic mode can be canceled at any time by pressing any button on the remote transmitter or by turning the ignition switch ON (II). The panic mode will not function if the ignition switch is ON (II). Keyless Entry System The security alarm system is integrated with the keyless entry system. The keyless entry system allows you to lock and unlock the vehicle with the remote transmitter. When you push the LOCK button, all doors lock. When you push the UNLOCK button once, only the driver's door unlocks. The remaining doors unlock when you push the button a second time. The ceiling light, if its switch is in the center position, will come on when you press the UNLOCK button. If you do not open a door, the light will go off in about 30 seconds, the doors will automatically relock, and the security system will rearm. If you relock the doors with the remote transmitter within 30 seconds, the light will go off immediately. You cannot lock the doors with the remote transmitter if a door is not fully closed, or if the key is in the ignition switch. If the doors will lock and unlock but the Security System will not arm make sure the trunk and hood are closed. If the doors will unlock, but not lock, the system may think a door is open. Check the door switches, the dome light operation, and the safety indicator. To open the trunk, push the Trunk Release button and hold it for about 2 seconds. The trunk will not open if the key is in the ignition switch. If the doors lock and unlock normally, but the trunk opener is inoperative or erratic, the problem could be a wrong remote or passenger multiplex control unit. 1998-99 remotes and control units are different than 2000-02 control units. Multiplex control units are also different for trim level and body style (coupe and sedan). If a third keyless/security transmitter has been added, the trunk release button must be pushed twice on that transmitter to open the trunk. The system will signal you when the doors lock and unlock by flashing the parking lights, side marker lights, and taillights: once when they lock, and twice when they unlock. Push the LOCK button twice within 5 seconds and the horn will confirm the car is locked with one short beep. If the lights do not flash, make sure the doors the hood and the trunk are closed and locked. Check that the security indicator blinks. If the Security Alarm System does not arm, see multiplex mode and input tests.

2- You can try resetting it with below procedure if you have not already .

Master reset Procedure

1- Disconect Battery Cables ( Negative & Positive Cables )you can use any electrical wire as an extension if battery cables don't reach .

2- Hold cables Together for 60 secs ,then let go

3- Wait 15 minutes

4- Make sure all doors are closed

5- Reconnect battery Cables

6- Lock & unlock the vehicles using the key from driver door side (if you have a key fob with no blade key, just lock & unlock using the key fob buttons)

7- Enter the vehicle and attempt to start

Please let me know

Thank You

Chad Farhat

ASE Certified Technician

Customer: replied 11 months ago.
Using Mitchell Pro Demand I check the powers and ground circuits of the immobilizer system and it all checks out. I did replace the immobilizer. System is functional some of the time, then the light will flash and no start.Are we saying the ECM is bad? I don't see anything in the schematic or in the initial explanation at the top of the page that involves the alarm system
Expert:  Steve replied 11 months ago.

I see the other person helping you opted out. Let's see if I can be of help, I do have some questions to ask you.

Just in case the key is bad, have you tried a different key? If you have other items on your key chain they can sometimes interfere with the the immobilizer system.

The other thing would be to watch the check engine light. When the car does not want to start, check and see if the check engine light comes on for 2 seconds and then goes off.

When it does not start what happens? Does it just start and die or seem to run as long as the key is held in the start position?

With the key on do the other indicators like the battery light come on with the key in the on position.

I know these are a lot of questions but your answers may help me with a solution for you

Customer: replied 11 months ago.
customer had small electronic key on chain. removed and works ok now. Fme.