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Discussion Starter · #1 ·
Hello all,

I recently acquired a manual 2006 TSX that cranks, but won't start. I've tried diagnosing several things that I will list below, but here are the most notable symptoms:
-Dash shows check emissions when the car turns on
-Cannot communicate to the ECU through the OBDII port
-Sometimes also shows VSA error
-(this one is weird, possibly related) odd intermittent buzzing noise under dash around relays, but NOT the relays themselves
-Fuel pump was just replaced, but seller reported fuel still wasn't being squirted from injectors

My first thought was to pull the ECU and see if there was any obvious corrosion. There was none, inside or out. I then plugged the ECU back in and checked all of the fuses and relays that I thought might be the issue (main, LAF, etc) but all of these were fine. I checked all easily accessible connections (to my knowledge), but again did not find anything. I also thought it may be an immobilizer problem, but the green key light on the dash goes away right after turning it on and does not blink.

Today after work I am going to look into that buzzing noise by the driver's footwell fuse box, as it is the only thing I have to go off of right now. Like I said, two known-working OBDII scanners were unable to communicate, so I can't even read codes to troubleshoot. I have a video of the buzzing noise if anyone would care to hear, but I'll be looking into that today and will report back here if I find anything.

Any ideas? I'm unfamiliar with Acuras and have searched extensively through forums for similar cases, but all of them seem to be immobilizer or ecu swap issues that don't apply here. Anything at all helps!
 

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Discussion Starter · #3 ·
Can you communicate with any module?
Sorry for the late response. Oddly, if I disconnect the battery and wait long enough, the car will turn on normally (key in second position) and I have comms with the ecm (no CEL or codes). As soon as I turn the key to the third position to try to start it, though, it will run for maybe two seconds before dying, throwing a CEL, and I lose communication with the ECU.
 

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Check the battery health? That buzzing sounds like a relay getting cycled rapidly, possibly because it doesn't have enough latch voltage or some module is confused. Obviously check static voltage but in this case I'd either use a battery tester (FLAPS if you don't own one) or hook up another battery.

HVAC off? Stereo off? Buzzing down there might be the speaker?
 

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Discussion Starter · #5 ·
Check the battery health? That buzzing sounds like a relay getting cycled rapidly, possibly because it doesn't have enough latch voltage or some module is confused. Obviously check static voltage but in this case I'd either use a battery tester (FLAPS if you don't own one) or hook up another battery.

HVAC off? Stereo off? Buzzing down there might be the speaker?
Thanks for the reply! The battery is relatively new, and I've hooked the whole car up to a charger to test that out as well. HVAC and stereo work, all other systems in the car do as well. Buzzing definitely isn't the speaker. Removing the main relay makes the sound go away. I tried swapping relays, buzzing persists. This weekend I changed the MICU, but that didn't change anything except that now the car won't even crank. Does anybody know which wires are for ground/power for the main relay socket? I'm thinking there's a short somewhere but don't know where to start looking.
 

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Try disconnecting the alternator, both b+ lead and 4 pin regulator connector and see if that changes anything
 

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Sorry for the late response. Oddly, if I disconnect the battery and wait long enough, the car will turn on normally (key in second position) and I have comms with the ecm (no CEL or codes). As soon as I turn the key to the third position to try to start it, though, it will run for maybe two seconds before dying, throwing a CEL, and I lose communication with the ECU.

Were you able to determine any DTC's while the ECU seemed to be working?

Since the engine cranks fine, your battery voltage is likely fine but connect a voltmeter to monitor battery voltage at all times.
I would also try to probe the ECU connectors to make sure the ECU is getting 12V.

Although you didn't find any corrosion on the ECU, it might be time to swap in another ECU.
Luckily a 2006 M/T ECU is fairly cheap, unlike a M/T 2007-08 TSX ECU.
 

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Discussion Starter · #9 ·
Were you able to determine any DTC's while the ECU seemed to be working?

Since the engine cranks fine, your battery voltage is likely fine but connect a voltmeter to monitor battery voltage at all times.
I would also try to probe the ECU connectors to make sure the ECU is getting 12V.

Although you didn't find any corrosion on the ECU, it might be time to swap in another ECU.
Luckily a 2006 M/T ECU is fairly cheap, unlike a M/T 2007-08 TSX ECU.
I was unable to get any DTC's, as when the ECU is in the "working" state, there is no CEL.

UPDATE:
I decided to pursue the buzzing noise that was coming from the main relay socket, and after a bit of tinkering around under there figured it wouldn't hurt to try replacing the MICU. Got the whole multiplex unit and replaced it, and now the symptoms have changed (honestly can't tell if it's for better or for worse). Now, the car will turn on fine in the second position, no buzzing from the main relay, the green immobilizer indicator goes away, and I have perfect comms with the ECU (although still no CEL to diagnose). The only BAD thing is that now the car won't even crank. Honestly at a complete loss now as to what it may be.

Couldn't find an ECU on ebay so I had to buy one at a relatively high price from a scrapyard to get shipped. I'm still really very skeptical that it's the ECU since everything looked fine and seems to function normally until the engine is cranked. As for checking pin voltage, I suppose I could try that if you think it's advisable...
 

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Thanks for updating your thread.
This is strange. Now at this point, your ECU appears to be ok.

The immobolizer/security system disables the fuel pump. The TSX engine will crank if the immoblizer is failing or the RFID/chip key is failing or not configured to the ECU.

I've never tried this, but there must be a way to jumper the TSX starter.
This may get the engine started at this point.

Swapping in a used ECU without configuring the immobolizer will allow the engine to crank but it won't start.


Edit: If you swap in the used ECU and the engine cranks you will have to tow it to a dealer to get the RFID/chip keys and immobolizer configured.

If the new ECU and MICU fixes the issue, I would suspect that someone jumped the car with the battery cables reversed and fried several electronic modules.
 

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Discussion Starter · #11 ·
Thanks for updating your thread.
This is strange. Now at this point, your ECU appears to be ok.

The immobolizer/security system disables the fuel pump. The TSX engine will crank if the immoblizer is failing or the RFID/chip key is failing or not configured to the ECU.

I've never tried this, but there must be a way to jumper the TSX starter.
This may get the engine started at this point.

Swapping in a used ECU without configuring the immobolizer will allow the engine to crank but it won't start.


Edit: If you swap in the used ECU and the engine cranks you will have to tow it to a dealer to get the RFID/chip keys and immobolizer configured.

If the new ECU and MICU fixes the issue, I would suspect that someone jumped the car with the battery cables reversed and fried several electronic modules.
I believe the previous owner experienced this issue while driving. Claims that the car just shut down in the middle of the highway. Of course, who knows if that's really true. I just don't know why swapping the MICU would've disabled the car from even cranking. What could've changed? I'm fairly certain I did everything correctly...
 

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Discussion Starter · #14 ·
Doesn’t the MICU have to be programmed/sync’d to the car (/other modules)?
I don't think it needs to be reprogrammed. Just replaced the ECU today and although I haven't gotten it reprogrammed yet, the VSA, check brake system, and check and system lights are still on. Also, the immobilizer indicator is flashing now as expected. It just doesn't seem like the ECU is the problem...

Also unplugged the alternator as suggested. No change. Only difference is the red battery indicator is now off on the dash (assuming the circuit just isn't complete now). Is it worth mentioning the oil pressure indicator is also on in the dash?

This is just bizarre. To make matters worse, I am on a time crunch to get this fixed or I will have to sell it off to someone else :/
 

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The alternator thought was before you swapped micu’s. I had a civic that had an alternator grounding issue. It would start and run but things would go haywire in the first few seconds of runtime. Disconnected the alternator and it was fine.

Double check that the micu doesn’t need some sort of vin matching with your original ecu in there first.
 

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Discussion Starter · #16 ·
The alternator thought was before you swapped micu’s. I had a civic that had an alternator grounding issue. It would start and run but things would go haywire in the first few seconds of runtime. Disconnected the alternator and it was fine.

Double check that the micu doesn’t need some sort of vin matching with your original ecu in there first.
Will confirm tomorrow. I do remember putting a fair amount of research into it and concluding that it's not needed, but it definitely can't hurt to double check. Tomorrow I'm going to put the original micu in and check the alternator ground. Thanks for the help so far!
 

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I don't suppose the engine now cranks with the new ECU?

Keep your scanner connected to the OBDII port until the issue is resolved and keep checking for DTC's.
Any DTC's with the new ECU installed?

A search on this forum with show that the TSX MICU has a low failure rate.
I only recall 1 other thread where the owner replaced the MICU trying to resolve an issue.

Re-installing the original MICU does sound like a good next step.
 

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Discussion Starter · #18 ·
I don't suppose the engine now cranks with the new ECU?

Keep your scanner connected to the OBDII port until the issue is resolved and keep checking for DTC's.
Any DTC's with the new ECU installed?

A search on this forum with show that the TSX MICU has a low failure rate.
I only recall 1 other thread where the owner replaced the MICU trying to resolve an issue.

Re-installing the original MICU does sound like a good next step.
It does not crank with the new ECU unfortunately, and no new DTCs are coming up. It seems as though the CEL only appeared after the engine ran for those quick 3-4 seconds before dying.

The rationale behind the MICU was the buzzing from the main relay socket regardless of which relay was in it. I figured it was either an internal short/bad connection or low power from whichever wire was feeding the main relay. MICU was cheap, so decided to go with that. Will be putting the original one in today.
 

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You should also check your body grounds inside the car. Pull kick panels, carpet, etc to find where the grounds bolt to the body. Sunroof leaks or other water intrusion can rust body grounds and you’ll get a lot of strange electrical gremlins.

Most times, the grounds for the dash harnesses will be low on the a-pillars on both sides of the dashboard.
 

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Discussion Starter · #20 ·
You should also check your body grounds inside the car. Pull kick panels, carpet, etc to find where the grounds bolt to the body. Sunroof leaks or other water intrusion can rust body grounds and you’ll get a lot of strange electrical gremlins.

Most times, the grounds for the dash harnesses will be low on the a-pillars on both sides of the dashboard.
Great advice. I downloaded the wiring diagrams for the car so I'll try to look at all the grounds I haven't touched yet. I will say though that I have already looked at the grounds associated with the ECU/micu and such.

One other thing (and I'm really just saying every small thing I've noticed at this point) is that the right bolt that mounts the ECU to the chassis was very rusted at the bottom, while the left bolt was not. Is this coincidence? Is the ECU grounded through it's chassis and the car's?
 
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