2000 Cadillac SLS SERVICE ENGINE LIGHT

Leaving a ground disconnected could result in the car not starting, or other symptoms as well. The check engine light is on for a reason, my guess is something is unplugged. Raise the hood and check for the obvious, the mass airflow sensor, in the air snorkel between the filter and the engine. It will run with this disconnected. If that is connected and you see nothing obvious, have it checked for codes. I can coach you through extracting codes if necessary, let me know.

No, the block heater shouldn't have anything to do with it. I'm assuming the car starts and runs, we just have a check engine light, right? Do this. With the key on, not running, push and hold the info button up, and the on/off together until we get into what is called segment check. All display segments will light, release buttons. It should show 'all?', Pushing info down will start scrolling through modules(aprox 22) in alphabetical order. Scroll until you reach 'PCM', push the info up, and you will either see 'PCM codes', or 'PCM clear codes'. Info down will toggle between one, or the other, we want PCM codes. When 'PCM codes' is on the info center, push info up to select. Have a pen and paper to write down which codes you have. You might have one, or multiple. It should say which is current, and which is history. Regardless, if there is multiple codes, let's clear them. Push on/off button and it should back up to the PCM codes/PCM clear codes option. Select clear codes with info down, and execute with info up, it should say codes cleared or no pcm codes. Cycle the key, and drive, or do whatever until the check engine light comes back on. Repeat above procedure, and this will relate to your fault. You can end diagnostics by turning the key off, or pressing any button on the left side(eng/met, info reset, etc. Hopefully this helps, there may be discrepancies in my instructions, since in the 11 years I have been with Cadillac, there have been some variances in the On-Board diagnostic architecture. Let me know your success

Each time you issue a clear codes, it resets the I/M flags to unready. I believe a p0404 is an egr fault, and if that is sticking wide open you will have rough run and potentially a p0101.

You didn't include a code number, is it still P0404? The diverter valves you are speaking of, are vacuum operated check valves. One is at the center of the rear bank(which is bank 1), the other is on a bracket at the water pump cover area. The bank 1/bank 2 term relates to which bank of cylinders #1 is in(Bank 1), or cylinder #2(Bank 2). When you start the vehicle, do you hear a pump run for a few minutes at the left front fender area? This would be your air pump, and it should run at startup.

Reviewing the information, you have dual air pumps. One is at rh fender, and one lh fender. In the under hood fuse box, there should be fuses labeled Bank 1 AIR and Bank 2 AIR(label is on the underside of cover). Check and see if the bank 1 fuse is blown. If it is not blown, check at startup if both pumps are running. The hose from the pump to the shut-off valves can be removed to see if there is fresh air flow from the pumps to the valves. You almost need a scan tool to do some activations and monitoring of o2 sensor change when the pumps are on to determine if the valves are working. If you can verify that both(or at least B 1) pump is working and air is present up to the valve, it is almost safe to say you have a faulty valve. The vacuum solenoid controls both valves at the same time, you would think if a solenoid was bad it would have codes for both, or a general AIR fault p0410. You also have relays for each pump to consider. If the fuse is blown for bank 1, you probably have a shorted pump, or most likely pump connector. Has this vehicle had the frame out of it, i.E. For oil leak correction/body work/or trans repair? Often times if the pumps have been disconnected electrically and reconnected, it reveals a poor connection that may have been fine until it was tampered with. If you have, and know your way around a hand vacuum pump, apply vacuum to the Bank 1 check valve with the engine running and the fresh air hose disconnected. You should have exhaust flowing through with vacuum applied, nothing when vacuum not applied.

As stated, the legend for the fuse block is under the cover that you remove to access the fuse block. It should be a large, clear, maxi fuse in a cluster of several the same style. You did not say whether the air pumps run at startup. I do not know costs, I am merely a person on the repair end. If you can do the diagnosis, you will save. If you don't pinpoint the problem, it is either going to cost more in unnecessary part replacement, or paying someone to diagnose it accurately. Try contacting the folks that put your engine in, see if they are willing to participate. They may be the cause of your grief although, the service procedure for engine replacement may have called for air pump removal or disconnect. It is from experience with cases similar to yours, that I don't disconnect the air pump(s) during a repair. The fuse may not be blown, it may be a poor connection at the pump. You need to determine that both pumps run, otherwise the proper diagnosis should include a scan tool that can read data, and perform special functions like commanding the pumps to run, and cycling the vacuum solenoid.