[johnnymo85]

Hey, all:

So last week my A/C stopped blowing and I got the service engine icon on my dash. On Friday while idling at a drive-thru I got dinging and my engine was overheating. My coolant was low so I added more coolant the next day. I checked the codes and I got the following0412, P0418, P0036, P0102, P0412, P0418, P0480, P0481 and assumed it was an issue with the radiator fan.

My brother and I checked all the relays/fuses and they al checked out good. We pulled the fan assembly out and when power is applied it runs fine. We let it idle and revved the engine some and it eventually started getting close to overheating but the fans never cut on. We attempted to charge the A/C but the compressor wouldn't cut on to allow us to. I drove it to work this morning (30 milesish) and it didn't start to overheat, but I wasn't sitting idling besides at a stop light...Any ideas? I'm taking it to a shop on Wednesday for diagnostics but I'd prefer to fix this myself.

 

[Submariner409]

Use this to decipher and post code definitions - we haven't memorized them all - yet !!

CTS-CTS-V FAQ: Cadillac On-Board Diagnostic Trouble Codes (OBD-II)

Yep - the P 0480 and P 0481 point to some sort of cooling fan problem. Maxi-fuse(s), relays ?? The fans should go to SLOW at about 218 degrees and FAST at about 230 or so. They're not needed above about 30 mph so that's why you saw no temp rise while driving steady-state. Maybe no coolant temp input to the PCM ? But look at the definitions for the P codes.......

I don't have a fan electrical schematic for later than 2005 - use www.alldatadiy.com for your year GM/Cadillac service manuals online. That should also have the fan on/off setpoints, too.

 

[johnnymo85]

Sorry, here's what the codes say:

P0412 Secondary Air Injection System Switching Valve A Circuit
P0418 Secondary Air Injection Control A Circuit
P0036 H02s Heater Control Circuit Bank 1 Sensor 2
P0102 Mass or Volume A Circuit Low
P0480 Fan 1 Control Circuit
P0481 Fan 2 Control Circuit

All the relays/maxi-fuses tested that they were functioning but it definitely seemed like a relay issue to me too...

 

[johnnymo85]

I have ordered a paperback repair manual ( that'll take a few days to arrive though), but any idea on how I would check the coolant temp nut to the PCM? Thanks so much for the help!

 

[Submariner409]

I fixed it - should have typed "input" instead of "nut".

The ECT (Engine Coolant Temp) sender is down low on the right (rear) bank rear (driver's) end of the block - just about in front of where your gas pedal toes would point.

 

[johnnymo85]

FYI I got this resolved. The wiring harness runs under the rack and pinion steering and when turning the steering wheel it was causing wires to break. I had a shop replace the wiring harness and reroute it and it fixed most of the issues. Still having an issue with my TCM...

 

[Kikoman]

My 2007 DTS has the exact same symptoms as you experienced -- can you provide any additional details as to what harness was replaced? I have thoroughly inspected and can't find any chafed or damaged wiring and I believe there is only one main harness in the engine compartment (P/N 25813746) and it lists for $1400+ thru GM...Thx!

 

[BoyMadison]

Yeah I too have been experiencing the exact same thing with my 2006 model. I would be interested in knowing what harness it was that you replaced also.

 

[Kikoman]

Check the wires at the top of the engine on the passenger side where they run down to the O2 sensor mounted in the tailpipe -- mine were frayed and had shorted to ground. Then check fuse #F21 to confirm it is not blown (mine was), replace if necessary. Good luck!