A few weeks back my parents were driving over to visit when their CTS lit up a Service Engine Soon light and the A/C began to blow intermittently warm air. Now, for anyone who’s ever had this happen to you, there are a couple of items to remember… First of all, stay calm. Cars typically don’t explode spontaneously, so it’s probably a good bet that you’ll be okay. Secondly, keep your eye on the gauges and try to assess if the vehicle is in immediate trouble. Luckily my dad is a pretty astute guy, so he kept his eye on everything and made it just fine.

Upon arriving he gave me the breakdown of what happened. Basically, we have an SES light that came on, slight operating temperature spike, slight oil pressure drop, and the intermittent A/C cooling. After letting the CTS sit for a few hours, we started her back up and she seemed fine with the exception of the A/C. I was able to pull the engine codes and got a P2601, which is an auxiliary fan failure. This made sense to me as you’d see an operating temperature spike when stuck in traffic, which they were. The lack of airflow would then cause the performance drop in the A/C… This all seems to follow a logical pattern. So let’s get to the repair.

A bit of research and snooping around the Cadillac forums yielded that this comes across as, if not a common occurrence, at the very least nothing to be surprised about. There is a potential for the problem to be a programming issue which would require a dealer update, but from what I could tell that’s specific to 2008 & older models. Searching for the part was rather surprising, as I was expecting “water pump” pricing (i.e. closer to $100). In actuality, the auxiliary pump is quite small, and that’s reflected in its price point. I ended up purchasing it through Amazon (ACDelco 251-721 GM Original Equipment Auxiliary Water Pump). 

When it got to my house, sure enough, the pump is pretty tiny. While this should make it easier to replace I feared that it’d be difficult to get to, as it could be located in a small nook or cranny. Luckily though, the repair went without a hitch.

First off, to locate the pump you’ll need to remove the shrouds covering the engine bay. You don’t need to take it all off, but it’s definitely easier if you do. After all the plastic is out of the way the pump is attached to the radiator on the passenger side. Once you locate it you’ll want to disconnect the electrical harness. Note that the plug does not have a pressure release point like most electrical connections. Instead, it has this metal clip.

The clip is actually quite simple to remove. I grabbed the broadside with a pair of nose pliers and pulled the clip off completely. To reinstall place the clip back on the loose connector prior to plugging it in. With the clip on, the plug becomes secured at the point of installation.

With the pump disconnected, I then pried it off the radiator. You can use a large flat head screwdriver and just pop it off. It disengages very easily. At this point, the pump is loose and can be maneuvered to get to the hoses. Now, it seems to me that you could do the hoses in any particular order. I ended up pulling the bottom one off first and then the side one. I take these kinds of pressure clamps off with an open-end adjustable wrench. I’m sure somewhere out there there’s a specific tool for this, but usually, you can just work it off.

Like most coolant hoses, they tend to get a little sticky. You can loosen them up a bit by using the same wrench and just rotating the hose on the pump “nozzles”. This will break any calcified liquid keeping the hose in place. From here on out it really is quite simple. Pop off the hoses, install the hoses on the new pump, install pump in radiator bracket and plug it in. Finish off the repair by placing the engine shrouds back on and the mechanical aspects of the repair are done.

The last step is to clear the codes. Luckily, I have a very nice code reader (which I picked up on eBay for about 25% of what the local autopart store wanted for it). As such, clearing the code is as simple as punching a few buttons. If you don’t have a reader though, disconnecting your negative ground battery cable for a bit should do the trick. Done and done.

Now for the moment of truth… I crank her over and… SES light is gone! Looks like it worked. Turn on the A/C and I’m greeted with a blast of cold air… for about 10 seconds. Guess what? Intermittent hot air is back; looks like we’re not done after all.


Join me in the next post as we tackle changing a defunct radiator fan motor.

Useful Parts & Tools to Help you with this DIY Project: