DIY: Bypass GM Block Heater Thermostat
 

I have a 2012 Cruze Eco and I ordere the oil pan heater as an option. I was under the impression it was actually a block heater when I ordered it, but it is nothing more than a small 200W steel heating elememt pressed to the side of the oil pan. It was only a $65 option, so I can't complain too much.

This oil pan heater does exactly what it is supposed to do and nothing more; it keeps the oil warm during extreme temperatures.

GM has installed an in-line thermostat switch that only allows the heater to work below -18C (0F). This is done to avoid confusing the cold start diagnostic tests, one of which compares the readings of the IAT and ECT sensors at start-up. If certain conditions/discrepancies are present, a DTC is set.

I wanted to use the heater at any temperature, so I bypassed the thermostat switch. Here's how if you're interested in doing the same.

BEFORE BEGINNING, READ CAREFULLY:

1. This may result in setting a P0116 code. Read up about this condition here, post 36 and 42:

5.3L engine block heater - Page 3 - Ask the GM Technician - GM-Trucks.com - Page 3

2. Your oil pan heater cord is expensive to replace and this is a permanent modification requiring soldering to get it functional once the thermostat is removed.

3. You are modifying a 120V electrical circuit. Electric shock, short circuits, damage to your vehicle's electrical system, and FIRE are allrisks you need to fully understand before doing this yourself. Do not proceed with this unless you are comfortable. Do not blame me if this doesn't work out. YOU HAVE BEEN WARNED.

Step 1, pull the round plastic thermostat cap off using pliers and a back and forth rotating motion. I used a rag to keep from marking up the plastic. You will see the top of the thermostat. Using your pliers, gently pull the thermostat out while twisting back and forth. Doing this will permenently pull apart the crimped connections on the thermostat, so go slow and be patient, twisting and pulling gently until the contacts pull apart. You should have something like this when done:

http://i52.photobucket.com/albums/g2...ps82d39c6f.jpg

Now bend up the little tabs and solder a piece of 16ga (minimum) wire across the terminals:

http://i52.photobucket.com/albums/g2...psd324fc82.jpg

Now push the cap back on using the pliers and rag. This will take a little effort and patience, just keep pushing and twisting, and you might have to push the rubber plug material up a bit also:

http://i52.photobucket.com/albums/g2...psc69ae9b2.jpg

Once you're done it helps to check your work by plugging into a power meter to make sure everything is working OK:

http://i52.photobucket.com/albums/g2...ps18b03840.jpg

This process will work for the Cruze and any other vehicles that use the same plug with the integrated thermostat switch. HOWEVER, the heater on the Cruze is only 200W and so far has not caused any issues with start up diagnostics. I would strongly reccomend finding out how powerful the OEM heater is on other GM vehicles before performing this modification. A more powerful heater, or an actual block heater that directly warms the coolant, may pose a higher risk to messing with the start-up diags.

For those interested, here's the condidions surrounding the P0116 code.

Running the DTC:
-Ignition is ON
-DTCs P0112, p0113, P0116, P0117, P0118, P0128, P0502, P0503 are not set
-Start up IAT (Intake Air Temperature) is greater than -7C (+20F)
-Engine is turned OFF for greater than 10 hours
-DTC P0116 runs once per drive cycle when the above conditions are met

Setting the DTC:
-Start up ECT (Engine Coolant Temperature) is greater then the IAT by more than 100C (180F)
OR
-Start up ECT is greater then the IAT by more than 15C (27F), then the vehicle is driven over 24 km/h (15 MPH) for 400 seconds, during which time the IAT does not fall by more than 8C (14F). If IAT falls more than 8C (14F) in that time, a block heater is detected and the test is aborted.
-DTC is set upon two consecutive drive cycle test failures

I'm not sure what happens after the DTC is set? Does the computer ignore the ECT sensor reading and go into some sort of limp mode? Does it soldier on using the values returned by the (apparently faulty) sensor? I'm not sure... perhaps a GM tech could look into this for us?

Other Cruze owners may wish to check out the original thread I created on the Cruzetalk Forum:

DIY - Oil Pan Heater Thermostat Removal

Thanks for posting this, Blue Angel.

How long do you leave your cruze plugged in before you unplug it and drive? I guess what im asking is what is the time vs. temperature gain on the oil pan heater?

If I had any doubts about whether I wanted this mod to be permanent or not, I'd leave the 'statted plug alone and cut it off altogether with enough lead wire to reattach it if desired, and graft a different plug on there or even use a clamp-on replacement plug.