HELP - Only Starts with Camshaft Sensor Disconnected

[evanw0920]

Hello everyone, I’m here seeking advice for my 2007 Chevrolet Suburban LT 1500 5.3L FlexFuel. I’ve been experiencing an issue where the engine cranks but won’t start. The only way I can get it to start is by disconnecting the camshaft sensor. I’ve already replaced both the crankshaft and camshaft sensors, but the problem persists. Additionally, my scanner isn’t showing any codes. Any suggestions or advice would be greatly appreciated. Thank you in advance!

 

[Fless]

Will it run if you start it with the cam sensor disconnected, but reconnect it? If so, then do a CASE relearn with a capable scanner.

 

[evanw0920]

Will it run if you start it with the cam sensor disconnected, but reconnect it? If so, then do a CASE relearn with a capable scanner.

Yep, i've tried doing that and the issue still persists

 

[Geotrash]

Yep, i've tried doing that and the issue still persists

What kind of scanner are you using?

 

[evanw0920]

What kind of scanner are you using?

innova 5610

 

[Geotrash]

innova 5610

That should have gotten the case relearn done properly for you. My suspicions are:

1/ Did you use Genuine GM sensors from a known good source (e.g not Amazon or eBay)? We’ve seen a lot of trouble here with aftermarket sensors.

2/ If yes, I suspect either a wiring problem or a problem with the ECU, but a wiring problem (e.g. damaged or broken wire) is much more likely. There is a troubleshooting procedure that includes checking the voltages on the pins at the cam position sensor. Do you have a meter and the ability to do that sort of testing?

 

[evanw0920]

That should have gotten the case relearn done properly for you. My suspicions are:

1/ Did you use Genuine GM sensors from a known good source (e.g not Amazon or eBay)? We’ve seen a lot of trouble here with aftermarket sensors.

2/ If yes, I suspect either a wiring problem or a problem with the ECU, but a wiring problem (e.g. damaged or broken wire) is much more likely. There is a troubleshooting procedure that includes checking the voltages on the pins at the cam position sensor. Do you have a meter and the ability to do that sort of testing?

I actually had GM OEM sensors delivered yesterday, haven't put them in yet.

I did check the wiring for the sensors and did get continuity but I might've done it wrong.

 

[Geotrash]

I actually had GM OEM sensors delivered yesterday, haven't put them in yet.

I did check the wiring for the sensors and did get continuity but I might've done it wrong.

Continuity is necessary, but you also need a 5V reference voltage on one of the pins. I’ll see if I can find the troubleshooting guide.

 

[evanw0920]

Continuity is necessary, but you also need a 5V reference voltage on one of the pins. I’ll see if I can find the troubleshooting guide.

Thank you, I'll look forward to looking over that guide.

 

[Fless]

See the link below and scroll down to the second diagram (Engine Data Sensors - 5-volt and Low Reference). Dead center is the Camshaft Position sensor and it shows the wire colors for the 5v Ref #1 (D-BU) and the ground (BN). That 5V Ref is shared by a few sensors on the left side of the diagram, but from different ECM pins.

Electrical Diagrams — 2007 Chevrolet Suburban 4WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Suburban 4WD V8-5.3L.

charm.li

 

[Geotrash]

See the link below and scroll down to the second diagram (Engine Data Sensors - 5-volt and Low Reference). Dead center is the Camshaft Position sensor and it shows the wire colors for the 5v Ref #1 (D-BU) and the ground (BN). That 5V Ref is shared by a few sensors on the left side of the diagram, but from different ECM pins.

Electrical Diagrams — 2007 Chevrolet Suburban 4WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Suburban 4WD V8-5.3L.

charm.li

Thank you, Steve. You saved me from digging.

 

[evanw0920]

See the link below and scroll down to the second diagram (Engine Data Sensors - 5-volt and Low Reference). Dead center is the Camshaft Position sensor and it shows the wire colors for the 5v Ref #1 (D-BU) and the ground (BN). That 5V Ref is shared by a few sensors on the left side of the diagram, but from different ECM pins.

Electrical Diagrams — 2007 Chevrolet Suburban 4WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Suburban 4WD V8-5.3L.

charm.li

Thanks, will try this out and get back to y'all.

 

[Fless]

Thanks, will try this out and get back to y'all.

I hope it helps. Seems like a short or lost ground on a circuit like that would set some kind of code.

 

[evanw0920]

I hope it helps. Seems like a short or lost ground on a circuit like that would set some kind of code.

Hey guys, finally got the new sensors in to no avail. I did test the wires and there was 5v. Still just cranks but doesn't start unless I unplug the sensor. Still no codes either.

Is the only other possibility an issue with the ECU?

I did check the timing chain and it hasn't jumped timing.

 

[evanw0920]

A couple of updates.


We have replaced the ECU, as another issue came up with the throttle body, which the new ECU did fix. Sadly, it did not fix the no-start unless cam sensor is unplugged issue.

Still just a crank, no-start condition.

Still not getting any codes

Is there anything specific that we should check or recheck, to hopefully fix this issue?

Thanks in advance.

 

[Fless]

Has a successful CASE relearn been done with the new ECU?

 

[evanw0920]

Has a successful CASE relearn been done with the new ECU?

Yes, it has.

 

[evanw0920]

Hello everyone, just a couple more useful updates.

We replaced the Fuel Pump - originally replaced it in 2023 but replaced it again as it was under warranty and we wanted to see what happened.

After replacing the fuel pump, it actually started multiple times with the sensor plugged in, but then it stopped working again with it plugged in ??

 

[evanw0920]

Zero Compression on Cylinder 3 as well.