Thread Title: 2009 H3 3.7L – Temp Gauge Works Cold But Dies Later + ABS Codes

Post:
Hey guys, looking for some advice on my ’09 Hummer H3 (3.7L I5).

I recently replaced the coolant thermostat because I was getting a P0128 code (engine not reaching proper operating temp). After the replacement, things seemed better — when I start it cold in the morning, the engine temperature gauge reads accurately and climbs like normal.

Here’s the weird part: later in the day, after driving or restarting, the gauge stops working. It’ll sit dead, like it’s not getting a signal anymore. Almost as if the sensor or gauge drops out after warming up.

I already replaced the coolant temp sensor (ACDelco, so OEM quality), and it worked fine for a few days, but then the issues came back. Coolant level is good, system was burped, and I just installed the new thermostat.

On top of that, I’m also chasing some ABS codes:

• C0268 – ABS Pump Motor Circuit Open/Shorted
  
• C0244 – PCM Indicated Reduced Engine Torque
  
• C0710 – Steering Wheel Position Sensor Circuit
  
• C0899 – Device Voltage Low
  
• U1000 – Class 2 Communication Malfunction
  

From what I’ve read:

• P0128 + gauge issues → thermostat or wiring/sensor problem.
  
• C0268 seems like the main ABS fault (pump motor circuit).
  
• The other C-codes and U1000 might be related to low voltage or grounding problems.
  

Battery and alternator seem okay on a quick check, but I haven’t load tested them yet.

Has anyone seen the temp gauge cut out after warm-up like this? Could it be a wiring issue to the cluster/ECM instead of the thermostat or sensor? And for the ABS — should I chase the pump motor circuit first before worrying about the steering sensor and comm codes?

Any input or similar experiences would be appreciated.

Thanks,
Kyle

 

• U1000 – Class 2 Communication Malfunction

I would start here. If the comm isn't talking nothing is going to work.

Clear all codes . Then rerun codes again. If comm code comes back make straight to the dlc. Check to make certain you have ground and positive. That the Class 2 is working properly with a good oscilloscope. You should see 120ohms across the network using a dvm set to ohms. If not start breaking the network into sub parts. jmho

 

Lol by the way that's all I got.

 

Batteries do funky things before they die. Easy free test at the store. I had a 4runner that would flicker all the gauges and lights and I chased other ideas until realizing it was just the battery.

 

OK, let's beat the dead horse Battery Terminal Connectors..... Are you still trying to use the crappy azzed OEM Battery Terminal Connectors? If so, hack them off and replace with a quality aftermarket set, like Stingers or your favorite brand. THE #! MOD to do to every H3/H3T. Know defective parts leading to all kinds of electrical Gremlins.

 

My 2009 also does this when really cold always in the 20’s in winter - never in warmer temps. Warms up, gauge works for a while, then cuts out and AC OFF code comes on - wierd! Next start up is fine depending on outside temp.