intermittent P0340 code on 1998 Malibu 3.1

My 98 Malibu 3.1L with 110,000km has had the check engine light come on almost every day for over a year.

I had a tune-up a few months ago where the where the plugs & wires, egr, air & fuel filters were replaced.

The check engine light still came on the following day. I had it scanned and it is P0340 Camshaft Position Sensor Cirtcuit Malfunction.

The car appers to run fine, with the exception of very poor gas mileage while city driving in stop & go traffic (only getting 250 km to a tank). Highway driving gets me over 500km a tank. Is it worth spending the money to have the wiring and camshaft sensor checked out? I don't want to needlessly spend money on something that isn't an issue.

Is it worth it? Only you can answer that. Right now, you likely have a minor problem such as oil from a leaking timing cover getting on the sensor. You can get the problem diagnosed at a time and place that is convenienient to you. Sooner or later the problem is going to get worse and leave you stranded. Then you won't have a choice about when and where to fix it.

If most are convinced there is something wrong with the sensor (or wiring) I don't have an issue replacing it. I just want to avoid spending time and money in a shop trying to diagnose and fix a problem that may not have any impact on how the car performs.

What does the computer getting a camshaft sensor malfunction mean to the operation of the engine? Could it be responsible for poor fuel consumption? I've had the O2 sensor replaced a couple of years ago and I don't know what else I could try to address that.

The cam sensor is mounted under the power steering pump and they do fail. The ecm uses the cam signal to fire the injectors. When and if it loses the signal the ecm uses a last known good signal so the engine will continue to run.

If the car didn't need the sensor than the manufacturer would not have put it on the engine. It synchronizes the fuel injection timing event at idle and low rpm's so it can run sequential fuel injection which helps with fuel economy and emissions at idle and off idle. It can have an effect on fuel economy, but I would be more worried about possible stalling while driving. I have had one that the sensor would short internally and cause the car to stall while driving. Have you had the fuel injectors and intake system cleaned? Do you let the car idle alot?

I believe the intake was cleaned and there was fuel system tune-up done when I had the intake manifold gaskets replaced last year but I don't believe it included cleaning the fuel injectors. What's involved with that?

The P0340 code indicates that there is malfunction with the circuit. The car had a coolant leak for a couple of years (crappy GM gaskets) is it possible the coolant did some damage to the sensor wiring?

The way I use to clean injectors and intake systems is with a Motorvac fuel system cleaning machine. It uses a machine with a mix of strong cleaners and gas. The car is run on the machine for minimum of 30 min. In tank fuel cleaners that you buy at stores do no good. Possible coolant could have leaked into the harness and into the sensor.