Why are there no error codes here? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-01-2013, 11:40 PM   #1
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Default Why are there no error codes here?

I've bought a troubled Cadillac CTS 3.6L V6. Everybody thinks a timing chain has jumped time; it will turn over, but won't catch and run. It stumbles, like it wants to start, but never goes. We've seen both cam banks rotate through the cam sensor holes(so the chains are intact), and our iffy compression tester says we don't have compression on either bank (next step is to use a trusted compression tester). It seems we've diagnosed a timing chain off a tooth.

But all I'm thinking is, where are the error codes?

The engine dummy light comes on at start up, but goes out like there is nothing wrong. We've started it without the intake box (and sensors), without 2 of the 4 cam sensors, among other miscelanious unplugged sensors. Not to mention that there is little-to-no compression in 3 tested cylinders. The ECU should be overflowing with error codes.

What would cause a silent ECU in a situation like this? We were able to monitor accurate ECU data via the OBDII port (fuel, rpm, temps); the ECU isn't completely dead, although it may still be malfunctioning.

Or is it normal for a car that hasn't run in 3 months to 'forget' it had codes, and not throw new codes on crank attempts?
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Old 07-02-2013, 05:47 AM   #2
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The engine has to be running X number of seconds before any diagnostics can be done. I'm not even sure you can use a high end scan tool to watch sensors during cranking because the sudden drop in power causes havoc while polling data from the PCM.
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Old 07-02-2013, 09:39 AM   #3
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As Mike said, you need drive cycles for the codes to pop up.
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Old 07-02-2013, 12:27 PM   #4
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Thanks guys. That makes sense. Parallels the previous owner'* story too, and why there are no codes.
Just wanted to make sure. I'll tear into it this week. Hopefully, I find the chains off their marks.
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