PCM of NC
PCM Reprogram - July 19, 2014
Even though the H3's I5 produces a bit more power than the Montero's V6, it's sluggish at best with low RPM shifts with flat torque curves. I researched a number of mechanical mods to improve this (within my budget) and found that the most common - air intake upgrades, headers - yielded little change in performance and better fuel efficiency.
From various H3 user forums I heard about PCM of North Carolina and researched their service; they flash and reprogram the factory PCM (power-train control module) promising better throttle response and fuel efficiency, better shift points making better use of the torque curve, and more horsepower.
Sounds too good to be true, but having lived in North Carolina, it's been my experience to have never been disappointed with anything that comes from that state. So I made the order.
I opted for their loaner program where they send a unit to replace the factory PCM while it's sent back to NC for the tune. While their instructions are pretty specific on how to remove the PCM, GM's design of its plug interfaces isn't all that intuitive, so what follows is a bit more detail on its removal:
The PCM is located on the engine firewall on the passenger side behind the coolant and window washer reservoirs.
Looking from above the PCM's cooling ribs you can see the three plugs that connect to it. To disconnect the plugs, remove the red strap on each by pulling it up. It will detach fairly easily.
From a side angle of the PCM you can see the grey ribbed band that surrounds the plug. This band acts like a lever. With some coaxing, lift it up and over the plug.
The plug is engineered so that this lever mechanism unlocks a series of cleats that lock the plug into the PCM. Dust and dirt in the mechanism will make this difficult risking breaking the plastic lever, so it's not a bad idea to blow it out with compressed air. Once the level is lifted all the way up, two red tabs appear at the top if the plug indicating that the cleats are clear and the plug can be removed.
If these red tabs are not in the position shown above, the grey lever hasn't been completely deployed.
With the plug removed, the cleats can be seen.
The PCM is held in place by a bracket. It has two tabs on top that hold it place.
If during the removal of the plugs the PCM becomes free of the bracket like this,
...the plugs will not have the necessary resistance from the PCM module to be removed, so make sure the module stays locked in while removing the plugs.
If the tuned PCM is anything like the loaner, the reprogram is very significant.
July 25, 2014I've received and installed the upgraded PCM from PCM of NC and I have to say that the H3 has awakened. All that was promised has been delivered and then some - more torque and pull off the line and up the slope, remarkably better throttle response, better shift points on acceleration both on and off road, better use of low range exploiting the I5's torque. I've yet to get enough data on fuel efficiency, but I have to say for the price, the result is well worth it.
I'm baffled why the I5 H3 didn't leave the factory this way. Would have saved GM considerable grief in mediocre performance evaluations, perhaps even the demise of the marque.