I was due to have my belts including my timing belt and water pump replaced so I brought them to a local garage to have the truck repaired. Prior to this time, I was having an issue with not receiving enough heat during the winter months from the heater to keep the truck warm so I asked for the thermostat to be replaced also. Now that the belts, timing belt, water pump and thermostat have all been replaced, I am getting a check engine message on the dash. I have brought it back to the garage a couple of times and they taken a look at it again to see what the problem is, reset the check engine light and sent me on my way. Now, as I drive it, the engine light comes on again and the engine is running at high RPMs with the tachometer running between 5,000-7,000. Please advise.

I was due to have my belts including my timing belt and water pump replaced so I brought them to a local garage to have the truck repaired. Prior to this time, I was having an issue with not receiving enough heat during the winter months from the heater to keep the truck warm so I asked for the thermostat to be replaced also. Now that the belts, timing belt, water pump and thermostat have all been replaced, I am getting a check engine message on the dash. I have brought it back to the garage a couple of times and they taken a look at it again to see what the problem is, reset the check engine light and sent me on my way. Now, as I drive it, the engine light comes on again and the engine is running at high RPMs with the tachometer running between 5,000-7,000. Please advise.

First, what are you driving? Year, make, model and engine/trans..

Second, what was the code that set the check engine light?
You paid them, they should have told you what the code was.

Frankly, I'm thinking there is a sensor that either is out of range or inadvertently became damaged during servicing.

Let us know...

It is a 2000 Nissan Frontier, V6.

It is a 2000 Nissan Frontier, V6. The technician did not give the code that was triggering the Check Engine light to come on.

If the sensor is the problem, is that also what is causing the RPMs to run so high?

I hope you can find out what that code was and get back to us later.
Knowing what code will help pinpoint the component that could easily be the source of your vehicle's problems.

**Yes, a faulty or broken sensor can cause high idle. Find that code.**

Most auto parts stores will retrieve the code for free,just don't buy any parts from them come back here and post the exact code. Might be something they forgot to hook back up as well.good luck.

The codes that came up were the Knock Sensor and Heat Sensor.

If you cleared the codes, and they came back, check connector. You can test or replace at that point.

It can be a sensor problem... but does the check engine light comes on only when the car is hot or its on once you turn on the ignition??

I could be driving down the street or highway and the check engine light will come on or it could be when I turn the truck on in the morning... it varies. I have had it reset with the computer a few times already and the resetting lasts for a day or maybe two and then the check engine light reappears. When we put it on the computer, it came up as having the knocking sensor and the heat sensor. It was suggested that I do a reset by disconnecting and reconnecting the battery instead of through the computer to see if it is a more effective reset. If I were to replace the knocking sensor... where would I find it to replace it? How about for the heat sensor as well. Any other ideas?

I would purchase the Shop Manual(about &15-$20) for your year and model. It will locate those items, and save you time and money in the future.

What is causing these sensors to be triggered? There was no problem before this and now there is one. Is it possible that there is an underlying cause that is not remedied by changing the sensors?

I'm not sure what you mean by "heat sensor." Are you referring to the coolant temp sensor? What are the exact codes that are being stored?

The codes that came up were the Knock Sensor and Heat Sensor.

What were the actual codes?
Was the root cause diagnosed? Or more likely, the component simply replace without looking at the circuits that can affect the sensors?

Hands on diagnosis of the sensor circuits and module is critical to pin-point the fault.