Home OBDII Doctor Chevy P1258 Trouble Code – Service your Express ECT

Chevy P1258 Trouble Code – Service your Express ECT

March 22, 2019

While this guide will help you erase your Chevy P1258 trouble code, you can also use it to replace your coolant sensor. If you have found this DIY How To Guide, chances are you are having overheating problems with your Chevy. If your Chevy van or truck is showing a very high temperature, but it doesn’t seem as though your engine is overheating, this is a common issue.

Your engine seems to be acting normally, you don’t have a boiling over coolant tank, and there’s no white smoke coming from your tailpipe. When you use a scan tool to check your OBDII trouble code it comes back as a Chevy P1258 check engine light. The specific language behind this code is Engine Coolant Over Temperature.

When this happens in your Chevy or GMC, but your engine doesn’t seem to be overheating it’s more than likely your Engine Coolant Temperature sensor that’s gone bad. To double check I’ll be showing you how to replace this unit in your 2006 GMC Express with a 5.3 liter Vortec engine in it.

This is a problem code that should be taken care of if your engine is not overheating. The Chevy P1258 trouble code will trigger your Protect Mode Active Engine condition. Which is when your Chevy engine computer determines that the engine coolant sensor is sending more than a 268°F temperature. Your GEN III GM engine will run with lowered ignition spark to help protect the engine as the Powertrain Control Module (PCM) attempts to salvage the engine or at least limit the damage to the engine.

To begin this guide, you will need to remove the 10mm bolts that run across the front of the engine bonnet. Because your Chevy Express ECT sensor is located on the driver side of the engine and behind your intake tract, you will need to remove several parts of your intake to access this sensor.

Once these bolts are removed, you must then unplug the MAF connector.

Pull up on the silver locking tab to unlock the Chevy Express MAF connector. Now pull gently to remove and unplug the MAF itself.

Now you can undo the clamps that hold the intake tract to your throttle body. Gently rotate the intake piping up and outward to remove the entire engine intake. Although you can get away with not removing the coolant overflow tank, you can do this to get yourself some more clearance.

Now with the intake out of the way you can peer down into the driver side of the engine to locate your coolant sensor. Reach down and unplug the two pin connector and then you can unscrew the engine coolant temperature sensor.

Replace your ECT sensor and replace it, making sure not to damage the threads or cross thread the new sensor in place. Reconnect your ECT connector and then use a OBDII scan tool to clear your check engine code.

Once you are done, put your MAF and intake piping back in place and plug it back in. Start your Express engine and allow it to warm up. Make sure that your Chevy P1258 check engine code does not return, and that your coolant temperature gauge reads properly.