I've read through alot of posts and haven't found anything like this... I have cleaned the EGR valve and MAF sensor. I could not find a MAP sensor. My Haynes manual isn't real specific.

I have a 2000 blazer witha V6 and 4wd. My wife was driving on the interstate and she said the tach and engine surged a few times. She said the tach quit working and the truck continued to run roughly. I was at my firehouse and asked our department mechanic if he had any ideas. He said it sounded like a transmission problem. After reading all of the posts here, I think it is probably a sensor of some kind. I used an electronic cleaner and sprayed the MAF sensor. I also used a carb cleaner on the EGR valve. I haven't found any posts on a tach that quits.

Any and all help would be appreciated!

Chuck

 

I guess everyone is as stumped as I am!

 

P0102 - Mass or Volume Air Flow Circuit Low Input
P0340 - Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor)

I believe that the CMP sensor is used in the tach input. It is located in the distributor under the rotor (CLICK HERE for a thread on this subject).

[quote]P0340

CIRCUIT DESCRIPTION
The Camshaft Position (CMP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CMP sensor with signal and ground circuits. Ignition voltage is supplied to the CMP sensor by an independent circuit. The CMP sensor produces a magnetic field whenever the ignition is ON. The CMP sensor is mounted near a reluctor wheel that is attached to the distributor shaft. When the distributor shaft rotates, or when the engine is cranking or running, the reluctor wheel changes the magnetic field. The CMP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CMP sensor detects per camshaft rotation. The control module uses the CMP sensor signal in order to calculate the correct timing for sequential fuel injection.

If the VCM does not detect the CMP signal while the engine is running this DTC will be set.

CONDITIONS FOR RUNNING THE DTC
The engine is running.

CONDITIONS FOR SETTING THE DTC
The CMP sensor reference pulse is not detected once every crankshaft revolution.

ACTION TAKEN WHEN THE DTC SETS

* The control module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
* The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.

CONDITIONS FOR CLEARING THE MIL OR DTC

* The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
* A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
* Use a scan tool in order to clear the DTCs.

DIAGNOSTIC AIDS
Electro-magnetic interference from the ignition coil or the spark plugs wire could cause a poor signal condition in the CMP signal circuit to the VCM. Ensure the routing of the CMP sensor circuitry is correct. Also check for the installation of aftermarket accessories and harnesses creating an electro-magnetic interference.

Refer to Symptoms. See: Symptom Related Diagnostic Procedures

An intermittent may be caused by any of the following conditions:

* A poor connection
* Rubbed through wire insulation
* A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Diagrams.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Diagrams.



TEST DESCRIPTION
The numbers below refer to the step

 

Thank you very much! By reading that, I believe that explains the tach quitting and it running rough occasionally. Would it also explain the P0102? I'll check the wiring and replace that sensor and see if that solves the problem. Thanks again.

Stay low and safe,
Lt. Benslay

 

The P0102 code could be caused by a dirty MAF sensor. This can happen over time even with a paper air filter, but happens much more quickly with an oiled aftermarket filter (k&n, etc). There are quite a few threads on the cleaning procedure, but if you have any questions, post up here.