Hi guys,

I'm new 1) here 2) to owning a hummer 3) to posting in any forum. I'm also not a car expert, but I'm a tiny bit above average when it comes to cars.

Background: bought a 2007 H3 about a month ago with a check engine light on. Scanned it and it's P0128. Gauge will go up to 1/4 only, heater and everything is fine. Clear the code and maybe a week or more later I got it again, cleared it again. So no engine light at that point.

So I parked the car outside one day in a -35 degrees weather and it didn't start after. Obviously I thought it's the battery and tried to jump start that didn't help. So I thought that something (fuel line) must be frozen. Towed it to my garage and waited a couple of days until temperature got to the positives (yes the weather is weird here). Added gas line antifreeze and tried again, still not working. it cranks, starter sounds good, battery is good, and can hear the fuel pump so that should be good too!

Called a mechanic to come see it, checked fuel pressure and it was good (I think 50 PSI or something). checked spark plugs AND THEY WERE DRY! he sprayed some kind of a flammable gas and still didn't fire up. FUSE BOX HAS CORROSION, but I highly doubt that it's causing a problem because I can hear the fuel pump and everything seems working! I can't think of anything else!!

1) unrelated question, but is the P0128 caused by the CTS or the thermostat?
2) can this code cause the car not to start?
3) WHAT ELSE CAN IT BE?

Thank you guys in advance! help a poor guy out.

 

Check out this site if you haven't already


https://www.obd-codes.com/p0128


They state you should not see any issues with drivability which I would assume includes starting the engine. I'm an H2 guy so I don't know much about the engines in the 3's but hopefully that site helps you out a bit.

 

Don't rule out the fuse box because you hear the fuel pump, but I wouldn't start there. Sounds like there is no spark and no injector pulse. This could be caused by a security issue, but I'm not sure. Do a search on the forum for that. If the security is okay, use a good quality scan tool and get into the data stream and check for RPM when cranking. This checks the crankshaft signal. If it's good, onto the next step. Check fuses for a bad one. Check all of them because one fuse can supply to more than one circuit. Pull out an ignition coil and check for spark while cranking. My guess is no. If there is no spark it's time to get into the wiring. Use a voltmeter for now because I don't have a wiring diagram handy and we don't want to fry any modules causing more grief. The injectors should have a 12volt power with the key on. The ground is controlled by computer and is best to use a noid light, not a test light, to check for ground. The light should flash when the engine is cranking over. This is a start.
P0128 can cause a no start, but unlikely in this case. If the CTS reads full cold, -38, or something like that, it will flood the engine on a warm or hot day. Your thermostat is most likely the cause. It's a very common problem.

 

Thank you for your detailed input. I was thinking it's either injectors or coils as well since idling wasn't stable before all of that happens (sorry forgot to mention that).
I've read all posts with people having to wait 10 minutes for the security issue, but I don't think I have that.

But what does it mean that there is pressure in the fuel line but the spark plugs are dry? Does that indicate that the fuel pump is working but the injectors are clogged?

I changed the CTS for yesterday because it was easy, but I'll do the thermostat soon once I get the car to run.

 

Fuse box has corrosion. That opens a Big Ole Can of worms. You need reliable voltage to the PCM circuit, without that, you will have all sorts of problems. Too many to speculate about here.

Clean up the main fuse block connections and ground. If you are still using the OEM crappy azzed battery terminal connectors, get rid of those and replace them with a quality aftermarket set, like Stingers or your favorite brand.

How many miles on the odo? For your rough idle see this:
https://www.hummerforums.com/forum/h...what-do-33916/

 

P0128
1st Check to see if the A/C works.
Yes? Replace the ECT.
No? Replace the CTS.

1. Clear the code P0128 and verify the gauge and A/C works again.
2. If so, start by replacing the thermostat with the highest quality part available. Retest thermostat's operation.
Tech Tips: A code P0128 will cause the temperature gauge not to work and the A/C not to work because the computer does not know if it is a thermostat or coolant sensor reading that is wrong.
____________________________________________

This code will NOT cause a no start! Before/during/after you repair the above code, go and check the battery/fuse box/ignition switch connections!
GL

 

Btw, If you have a scanner:

1. Start and run the engine to operating temperature. Clear the DTC's.

2. Verify the actual temperature of the engine matches the scanner display.

3. If the values match, test drive the vehicle while monitoring the Engine Coolant Temperature Sensor.

4. If the actual engine coolant temperature drops to less than 176 F, replace the defective thermostat.

5. Clean the throttle body assembly.

 

You are indeed correct! Pass lock feature:
Yes: fuel pump,
No: injector pulse,
No: Spark..
You can't steal my rig, just my gas.

 

Thank you all for your responses! just wanted to update you since it's working again after I brought in a mechanic.

Apparently the cylinders were flooded! he's saying that the weather was extremely cold that the fuel didn't burn in time and just filled the cylinder. floored the pedal and kept on cranking for a while until the fuel was flushed and better mixture fired it up.

 

Regarding the P0128 code: it is the thermostat. I changed the CTS just because it was easy and didn't do much. I also plugged in an OBD scanner and the coolant temperature is at 75 degrees.

Does anyone know how to tighten the CTS? I can't find the right tool for it.