This 1999 S10 Blazer came in with the complaint that the engine would run poorly sometimes. The customer unfortunately could not provide a better description of the issue. Luckily there were some clear codes stored in the PCM memory, P0118 and P1115
Code P0118 was stored due to a high voltage signal from the coolant temperature sensor.
Code P1115 was stored due to and intermittent high voltage signal from the coolant temperature sensor. This intermittent code explains why the vehicle runs poorly sometimes.
The coolant temperature sensor is located on the driver’s side cylinder head, below the master cylinder area. It is a two wire sensor and if you look closely at the picture below you will see that the terminals are compressed. You may want to click on the picture to enlarge it. This compressed condition will allow the terminals to lose contact with the corresponding terminal on the coolant temperature sensor.
Looking at the data below with the coolant temperature sensor unplugged you will see a coolant temperature of -40 F. The coolant temperature is at 5 volts. To clarify the 5 volt signal is a high voltage signal as the sensor operating voltage range is from 0-5 volts.
I used a fused jumper wire to “short” the two wires together. The wire does not need to be fused but I happen to have one that has the correct terminal ends on it and it makes the process much easier.
With the two wires “shorted” together the temperature jumps to 302 F and the signal voltage drops to zero volts. This test confirms that the remaining wire and the PCM are both okay at this time.
I cut off the old harness connector and spliced in a new one. Note that I staggered the splice connections.
I used a small torch to heat the heat shrink tubing.
The wires are neatly back into the split loom and the harness is reconnected to the temperature sensor.
The coolant temperature at engine startup.
The engine temperature after about ten minutes of idling.
I cleared the codes and took this Blazer for a test drive. This one is fixed.