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Old 08-01-2019, 02:41 PM   #1
spotana98
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2006 VUE 3.5L
Default Starting and possible bad ECU

Hey all~

I hesitated greatly on posting for advice, because I haven't exhausted the troubleshooting steps that I know if. However, this is the situation.

2006 Vue 3.5L AWD with 206,xxx miles.
Worked one day. The next, went to start it, and it's cranking game was strong, but not the slightest intent to start. No firing, no nothing.

So maybe it's the ignition?
Maybe the Fuel Pump? - Engine didn't even kick, which I imagine if there were ANY fuel left from last start, it may have sputtered for a sec?

I haven't had any Check Engine lights or any other indicator that there was an impending issue.

In any case, I connected up my OBDII scanner, and while the ELM shows connected, it can't connect to the ECU. Tried several times, tried it in my two other vehicles without fail, but can't get the ECU to connect.

Maybe the ECU?
Checked all ECU, and for good measure, BCM fuses, which were all looking good.

Disconnected batter for several hours, in attempt to "reset" ECU, and nothing.

So as good as I can tell, I have a bad ECU, and it's !@#$%^& up my start and drive game.

Any suggestions? Is it likely that my diagnosis is correct? Any guidance would be greatly appreciated. I'm a weekend mechanic, but when it starts getting into complex electrical garbage, I'm out.

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Old 08-01-2019, 03:53 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: Starting and possible bad ECU

While ecms can fail, there are many tell tale indicators without needing a reader - the instrument panel gauges and indicators. ABS and air bag systems use their own modules to turn on indicators for state of health. The bcm operates the rest of the gauges but the ecm must send rpm signals (and several other sensor signals) to the bcm with the bcm driving the tach needle, temperature and oil indicator. During starting, engine rpm is derived from crank sensor signals sent to the ecm to allow the ecm to run the entire EFI system. The starter is conventional without need for the ecm. Security (Passlock) requires a password between the two modules to allow engine running. During starting, the tach should display rpm/needle movement as a sign of ecm operation. If starting doesn't show tach needle movement, a faulty crank sensor may be disabling the ecm. Crank sensor timing signals is the electronic heart beat of every ecm. Without it the ecm doesn't; turn on fuel pump, initiate ignition for spark and pulse injectors. The ecm doesn't communicate directly to generic readers as all comms go thru the bcm. GMs Tech II scantool has the capability to communicate (via canbus wiring) to each module.

A quick test of the ecm would be spraying starting fluid into throttle then starting. This provides fuel if a fuel issue is the problem. If spark is working, the engine should fire up for the amount of starting fuel fed. No startup may be a faulty ignition system (both coil packs), crank sensor or ecm.

If I'm not mistaken, the crank sensor is behind the timing cover. Sensor location is next the crankshaft. Yours may have dual sensors. Being difficult to access, troubleshooting is most likely the preferred method to determine fault before presuming a faulty crank sensor. Making it difficult to troubleshoot on a diy level without GMs scantool; testing for fuel injection operation and spark. The fuel pump operates at ignition ON time for a few seconds whether the engine is started or not. This allows a quick fuel pump and pressure test by simply depressing the fuel test valve on the fuel rail, expecting fuel to spray out under pressure (cover with a rag to catch fuel spray). Removing one bank of spark plugs will reveal whether or not injectors are operating. Several starting attempts should flood the engine with fuel. Plugs should be wet or smell of fuel, indicating fuel, pressure and injectors are operating. Injectors operating means the ecm is operating because the crank sensor is sending timing signals to allow the ecm to run.

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Old 08-01-2019, 05:43 PM   #3
spotana98
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2006 VUE 3.5L
Default Re: Starting and possible bad ECU

Thank you for the quick reply.

I will start the troubleshooting process, based on your recommendations. I was on the fence about the ECM just not being able to be read, and took that as an almost definite dead ECU issue, when it fact, it sounds like a generic scanner doesn't do much for GM vehicles. I started with starting fluid and nothing. I'm in the process of pulling a plug to check for fuel in the cylinder.

I did pat attention to the Instrument cluster. The gas needle doesn't move, as is the same for all of the others. The Tach barely ticks, but to say it doesn't move at all, would be a lie. The check engine and SES light stay illuminated, but I image that is the case until the vehicle is started?

...
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Old 08-01-2019, 06:51 PM   #4
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2005 VUE 3.5L
2007 VUE 3.5L
Default Re: Starting and possible bad ECU

I would check fuel pressure. See thumbnail to locate test port. Check for healthy spray if you don't have a gauge.

Its normal for CEL to remain on until engine starts.

Does your OBD device have live data function?

If yes select RPM and monitor for around 200 RPM when engine cranking (not viewable on tach).

RPM typically indicates crank position sensor (CKP) and PCM are alive and well.

02-07 Vue OBD uses KWPF protocol (KWP-2000) - European and Asian standard if you can manually configure code reader.
Attached Images
File Type: jpg 3.5 Fuel Test Port - edit 2.jpg (111.0 KB, 11 views)

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Old 08-01-2019, 07:05 PM   #5
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Default Re: Starting and possible bad ECU

Another clue - starting fluid didn't get the engine running. This suggests lack of spark otherwise volatile starting fluid would ignite to at least make the engine run for a second or so. This also suggests a fuel issue. Fuel and spark are needed to run engines. Its presumed air and compression are givens.

The engine symbol is the service engine soon light unless your Vue has 'SERVICE ENGINE SOON' as the check engine indicator. A separate wrench symbol lights up for non emissions error codes (generic readers cannot decode). It turned on as soon as something failed in the EFI system whether driving along or starting up.

From rockauto, parts show individual ignition coils for each spark plug. If so, testing for spark is easy. With a spare spark plug or using one removed from a cylinder, reconnect plug to ignition coil, connect to wiring and wire a jumper to ground the plug base to the engine block. Remove the fuel pump fuse or pump relay and have someone startup while you observe for spark across the plug gap.

Last edited by fdryer; 08-01-2019 at 07:12 PM..

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Old 10-04-2019, 04:48 PM   #6
spotana98
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2006 VUE 3.5L
Default Re: Starting and possible bad ECU

I might tackle the Crankshaft Position Sensor. I'm not keeping the car, but want to make sure it's running. I can't find a good instructional on how to remove it, other than doing searches for timing belt replacements. Does anyone know if the timing belt has to be removed to get the sensor off? Can the old belt and tensioner be put back in place? I've done timing chain kits on other cars, so I know how to align everything. I just don't want to sink the extra money into stuff that's still working.

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Old 10-04-2019, 06:17 PM   #7
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2003 L-Series 3.0L Sedan
Default Re: Starting and possible bad ECU

Search within these forums as there are two places for crank sensors hiding. 3.0L V6 engines have theirs next to the oil filter housing and as easy 15 minute repair. More time is spent following where the connection point is to disconnect and snake the replacement wire harness back. If I'm not mistaken, your Honda 3.5L V6 hides its crank sensor behind the timing cover, next to the crankshaft.

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Old 10-05-2019, 12:34 AM   #8
spotana98
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Default Re: Starting and possible bad ECU

Mine is definitely the 3.5L Honda engine. The Crankshaft Position Sensor is under the timing belt cover and it looks to be somewhat on the right of the Crankshaft. I canít tell if the belt had to be removed to take it off, though. I canít find step-by-step instructions to remove it. Only for the 3.0L and the 2.2L.

...
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Old 10-17-2019, 02:55 PM   #9
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2006 VUE 3.5L
Default Re: Starting and possible bad ECU

So very angry.

I got my genuine GM CPS today after pulling the old one. Hooked everything back up, and low and behold; same issue. Granted I didn't put the serpentine belt back on, but I reconnected the PCM/BCM/ECU (Whatever computer is under the hood mounted to the wheel well), but that shouldn't matter when trying to get spark/engine turn over. Also not able to connect to scan tool via OBDII port.

I don't even know where to go from here. I thought for sure I'd tested for no spark and no gas in the cylinders. When I turn the key on, the tach jumps up a little and goes back down. I was certain that my 200$ part was the issue.

Now what??!

...
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Old 10-17-2019, 10:22 PM   #10
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Default Re: Starting and possible bad ECU

I think you have to go back to the beginning. While some shotgunning of problems does have its advantages, shotgunning presumes knowledge of an outcome that's predictable. Shotgunning doesn't work all the time.

You have the option to make spark and fuel tests to verify one or the other is missing or working. Presuming several starting attempts occurred, spark and/or fuel is missing. Starting fluid failing to get the engine to run suggests an ignition problem. There's a small possibility of excessive fuel drowning spark wasn't helped with starting fluid if spark was already shorted from soaked spark plugs. Basic troubleshooting in my opinion would be visually verifying fuel on spark plugs and visually testing for spark. One spark plug and one ignition coil. Several if in doubt.

I'm not completely familiar with Vue factory security but if you have Passlock security, if it flashes during starting, Passlock disables injector operation. If security isn't flashing during starting, you can try verifying fuel and spark visually. At this point, it may be wise wise to do the leg work as one alternative is to have GM figure it out. Another might be hiring a mobile specialist capable of diagnosing/troubleshooting GM EFI systems. An above average repair shop is another choice.

As I see it, you've cut the problem into two areas by replacing the crank sensor. Either the ecm and bcm aren't communicating or one is faulty preventing the other from working or a fuel/and or spark issue is preventing the engine from starting.

Personally, I try diagnosing/troubleshooting as a diyer. I have a limited knowledge of electronics applicable to EFI systems and general knowledge of vehicle security systems (as long as I have an interest in evolving systems).

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