2001 Hummer H1 error code PO126
 

Hello all, I am new to this forum. Recently, I purchased a 2001 Hummer H1 with 24k miles. Rarely driven. Recently an error code of PO126 was read after the engine light came one, "Insufficient coolent temp for stable operation." Will I need to replace the thermostat? I've been told to drive it more often. Any suggestions will be great appreciated. Thank ypu

Common Problems That Trigger the P0126 Code

• Defective Engine Thermostat
• Defective Engine Coolant Temperature Sensor
• Defective Intake Air Temperature Sensor
• Defective Cooling System
• Low Engine Coolant
• Dirty Engine Coolant, causing incorrect Coolant Temperature Sensor readings
• Defective, always running Engine Cooling fan(s)

Thank you for the response. Will driving the vehicle do it harm. I will take it to the shop as soon as possible, but in the mean time, should I drive it. I know that's a hard question to answer. Thanks again.

Driving with an error code can do harm. Diy or take it to a shop to fix asap!

Thanks, appreciate your time.

Start with the easy stuff first. Have you checked the coolant level? If you don't have service records showing a coolant flush I would start by changing the coolant. If the truck set as much as it sounds like it did you may need have the radiator flushed out. I would also expect that seals/gaskets, etc front to back may need to be replaced. The sensors are easy to replace ( on top of the engine ) and require no special tools. You should be able to do the vast majority of this yourself at minimal cost.

Thank you for the response. I'm not very mechanical so you gave me a great starting point. Really appreciate any guidance and feedback. Thanks again.

Hope you have a large wallet and someone who knows how to work on these trucks. LOL
Most likely, your coolant was never changed and your old, original thermostats are stuck open. Start by having the coolant flush with the green stuff, not dexcool. Buy two AC Delco 195 stats and replaced your old ones. Where are you located? Northern part of the country?
In addition to all the great info that has been supplied already, I'll tell you an additional possibility, which I'm still currently experiencing with my truck just for info so you have some idea.
I replaced my radiator with an Aluminum radiator. Had it coated with Thermal Dispersing coating. Added a Bypass restrictor fitting to the water pump to increase the coolant flow to the radiator. Ever since I did this, over a year ago, I get the same code when driving during the cooler months. My thermostats are new and are properly functioning. When driving on the beach, my truck reaches 195 and the stats open up. When my truck had both my stats stuck open, it ran warmer than it does now!! I have a scangauge so I can see the temperatures clearly while this is happenning. My truck runs fine while the code is on. The code usually pops up after running the truck, shutting it and then restarting it. I'm now slowly working on different solutions to make my truck run warmer during the cooler months. Get yourself a OBD Scan tool from Harbor Freight in order to be able to read the code quickly once it comes on. You'll also be able to clear the codes.
So like 3Hummers said, start with the easier stuff and stuff that you would have to do anyways as part of your maintenance. There are two temperature sensors, one in the left head and the other near the thermostats. The low coolant sensor, is not cheap and it's located inside, on the bottom of the overflow tank.

My brother just put a low coolant sensor in his 2000 wagon. I think he paid about $150.00 through Dave at Hummerpartsguy.com

Thanks everyone, it's great to see all the support. Took it to the shop, luckily it was a simple fix. Coolent was added and the vehicle needs to be driven more. I appreciate all the feedback and assistance. Glad to see so many resources.