2006 Civic will only start with OBD connected
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2006 Civic will only start with OBD connected
Engine would turn over but not start. There was a clicking noise coming from the inside relay/fuse area. Replaced the PGM-FI relay based on some other DIY threads. No change. Decided to see if we could pull a code with a borrowed scanner. When we plugged it up and tried to start after getting 0 codes, it fired and ran fine. When we unplug the scanner, it shuts down.???
I bought a scanner to at least save me the tow bill. I'm also going to check the main grounds.
I bought a scanner to at least save me the tow bill. I'm also going to check the main grounds.
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I had exactly the same symptoms with my sons old civic 2001 ex. I had similar problems after me and my son replaced head gasket and had to disconnect a lot of wires and reconnect them during reassembly. After reassembly car would turn but would not start. Accidentally I plugged in scanner in OBDII port to see if I can read codes, cranked the engine and it started. Without scanner connected to OBDII port it would die right away. While running I read code P0505 - fault of Idle Air Control Valve. Also car was running erratically during low RPM idling. But because Car would not start without scanner connected to the OBD2 port - it means that scanner through the port provides ground to PCM to start the car properly.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
Last edited by AndreyG; Sep 27, 2014 at 06:27 PM.
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I had exactly the same symptoms with my sons old civic 2001 ex. I had similar problems after me and my son replaced head gasket and had to disconnect a lot of wires and reconnect them during reassembly. After reassembly car would turn but would not start. Accidentally I plugged in scanner in OBDII port to see if I can read codes, cranked the engine and it started. Without scanner connected to OBDII port it would die right away. While running I read code P0505 - fault of Idle Air Control Valve. Also car was running erratically during low RPM idling. But because Car would not start without scanner connected to the OBD2 port - it means that scanner through the port provides ground to PCM to start the car properly.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
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I had exactly the same symptoms with my sons old civic 2001 ex. I had similar problems after me and my son replaced head gasket and had to disconnect a lot of wires and reconnect them during reassembly. After reassembly car would turn but would not start. Accidentally I plugged in scanner in OBDII port to see if I can read codes, cranked the engine and it started. Without scanner connected to OBDII port it would die right away. While running I read code P0505 - fault of Idle Air Control Valve. Also car was running erratically during low RPM idling. But because Car would not start without scanner connected to the OBD2 port - it means that scanner through the port provides ground to PCM to start the car properly.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
Answer is - while doing repair you have a ground wire undone somewhere and did not secure it well after reassembly. In my case wire I did not secure was under the air intake box - not visible after Air Intake is in place. During assembly I pried the ground wire the bolt slightly but forgot to tighten it with the wrench. I spent a half a day looking for the problem and researching it on internet, finally after tightening this G102 ground connection - all went smooth and car starts without a diagnostic computer connected to OBDII port. Hope it helps someone with similar problem.
Re: 2006 Civic will only start with OBD connected 
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It seems as if this a common problem with these civic.
My 2002 civic ex,V-tec, have the same problem after I rebuilt the engine and replace the 4 bearings on the input shaft and secondary shaft Also . I finished put it back together on a Sunday afternoon and I drove it the Monday all day, the Tuesday after I got off work it starts and died about 40 seconds after I drove off. It start sometimes but it, shut off after and it will turn over but wont start.but if I connect the cable from the scanner to it it will start and run pretty fine ,even up until now that's what I'm driving with connected to my car.becaut I can't fine the problem.
My 2002 civic ex,V-tec, have the same problem after I rebuilt the engine and replace the 4 bearings on the input shaft and secondary shaft Also . I finished put it back together on a Sunday afternoon and I drove it the Monday all day, the Tuesday after I got off work it starts and died about 40 seconds after I drove off. It start sometimes but it, shut off after and it will turn over but wont start.but if I connect the cable from the scanner to it it will start and run pretty fine ,even up until now that's what I'm driving with connected to my car.becaut I can't fine the problem.
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Re: 2006 Civic will only start with OBD connected
Start looking, lots of people forget the important computer ones near the water passage. Make sure the meter is clean and shiny
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You talking the complete water housing that have the coolant hoses connected to it? If its that, I connect all the wires in that areas..I hope it's not the PCM Computer is bad even though I might have doubts that it is the computer, since so many people have the same issues and it turned out to be ground issues. I will check them today. Also, just yesterday I found out that I have no AC coming from the side vent in the car,only the ones where the radio at.
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Engine would turn over but not start. There was a clicking noise coming from the inside relay/fuse area. Replaced the PGM-FI relay based on some other DIY threads. No change. Decided to see if we could pull a code with a borrowed scanner. When we plugged it up and tried to start after getting 0 codes, it fired and ran fine. When we unplug the scanner, it shuts down.???
I bought a scanner to at least save me the tow bill. I'm also going to check the main grounds.
I bought a scanner to at least save me the tow bill. I'm also going to check the main grounds.
I’m have the same problem on a 01 Dodge Ram 1500. Did you figure it out? 😅
"Marge, anyone could miss Canada! All tucked away down there."
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The problem is the big goat on the front 
Jokes aside, the problem is usually that the engine is missing a ground connection. So make sure all the grounds are connected, and clean and tight
Jokes aside, the problem is usually that the engine is missing a ground connection. So make sure all the grounds are connected, and clean and tight
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so the same thing happened to me last year. I bet it is the main ground wire just above the thermostat on the water support on the left side of the engine infront the radiator..or just check all the ground wires and make sure that the surface where they're grounded to are clean and check to see if anyone of them loose if anyone loose thats the reason for your problem. Good luck.
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I strongly suggest checking your grounds as others have suggested. I had the same issue here:
Inconsistent Spark on All Cylinders after Engine Reassembly [solved] - Honda Civic Forum (civicforums.com)
When the OBD II reader is plugged in, one of the pins grounds the ECU/PCM. When you remove the code reader, it looses that ground and shuts down. This will leave some things working, like the starter, headlights, instrument lights, etc. The problem is that, without being properly grounded, the ECU cannot send spark to the cylinders consistently, if at all. This will fill up your cylinders with a bunch of gas, but the engine can't run without that gas being ignited.
You can check the strength of a ground as described in the video below:
Essentially, you're placing one probe of the multimeter on the negative battery terminal and the other on the ground you're trying to test. You should see very low resistance between the two probes on a good ground. Once you find a weak ground, I recommend cleaning up the areas where metal-to-metal contact occurs with electrical contact or parts cleaner. I used a brass or steel brush the clean corrosion and other grime off of the surfaces. The idea is to make it easier for the electrical contact to occur. Make sure any bolts or nuts holding the ground wire to the metal is tight enough to keep it securely connected so that the electrical connection will be strong.
It doesn't hurt to have your battery disconnected while working on this or on any electrical system.
Inconsistent Spark on All Cylinders after Engine Reassembly [solved] - Honda Civic Forum (civicforums.com)
When the OBD II reader is plugged in, one of the pins grounds the ECU/PCM. When you remove the code reader, it looses that ground and shuts down. This will leave some things working, like the starter, headlights, instrument lights, etc. The problem is that, without being properly grounded, the ECU cannot send spark to the cylinders consistently, if at all. This will fill up your cylinders with a bunch of gas, but the engine can't run without that gas being ignited.
You can check the strength of a ground as described in the video below:
Essentially, you're placing one probe of the multimeter on the negative battery terminal and the other on the ground you're trying to test. You should see very low resistance between the two probes on a good ground. Once you find a weak ground, I recommend cleaning up the areas where metal-to-metal contact occurs with electrical contact or parts cleaner. I used a brass or steel brush the clean corrosion and other grime off of the surfaces. The idea is to make it easier for the electrical contact to occur. Make sure any bolts or nuts holding the ground wire to the metal is tight enough to keep it securely connected so that the electrical connection will be strong.
It doesn't hurt to have your battery disconnected while working on this or on any electrical system.
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