Troubleshooting '97 V6 Taco 4WD M/T P0340: Camshaft Position Sensor Circuit Malfunction

I have been experiencing an intermittent P0340 error code (P0340: Camshaft Position Sensor Circuit Malfunction) on my '97 V6 Taco 4WD M/T for the past few months. The Taco appears to run fine despite the error code. The Camshaft Position Sensor (CPS) checked out as serviceable as per the FSM, but I replaced it anyway while changing the timing belt/water pump/etc. The Crankshaft Position Sensor also check out as serviceable & the crank gear with integral reluctor ring was changed with the timing belt. This Taco has seen a lot of hard off-roading in deep mud/high water its entire life. The OEM Diagnostic Flowchart did not call for it, but I also serviced the grounding points at the block/firewall/left fender. The female connector to the CPS was also disassembled/cleaned/inspected/reassembled. Just finished checking continuity in both circuits to the ECM and they appeared fine. Shaking the wiring harness showed no effect on the continuity. I felt sure I would find this intermittent problem to be at the female connector to the CPS. No Joy! The Flowchart says it is time to change the ECM. A rebuilt ECM is not available thru Toyota so will have to look into a rebuild of my original OEM DENSO unit (89661-04310). ECMGURU appears to do a good rebuild with lifetime warranty for $200, showing excellent feedback. Before I go down that road, can anyone think of anything else that might cause this problem other than a bad ECM? ECM damage/failure outside of water damage is supposed to be pretty rare. TIA!

EDIT: No obvious damage on the interior of the ECM but I don't have a trained eye to detect it. I would feel more confident that I have an ECM problem if it was a failure problem, not an intermittent problem. An intermittent problem points me back to a wiring issue such as the female connector of the CPS, which will be checked again before getting the ECM rebuilt.

 

These intermittent issues are always a problem. You are going to need to find a shop that can scope the wave form from the CPS at the PCM. The bitch is going to be having the scope hooked up and recording when it sets either a pending or an actual code. Take a REAL close look at the tit coming off the gear and see if it is damaged and run her to see if it runs straight and true.

In addition to the above, well, actually before you do the above, run a voltage drop test on all of the grounds for the PCM as well as all the grounds from the motor to the chassis/frame/battery. We are talking mA for the PCM. I have had early i.e. “old” Pathfinder that required additional grounds from the motor to the chassis, motor to the battery, because of old quasi corroded, over 1v drop in the wires in the harness. Am I an EE, no, I do know that after the additional grounds ALL the smog monitors ran and completed, the original complaint. This poor truck has been through the parts cannon and various shops before the truck given to me because she was cursed, possessed and had a hex put on her, seriously, thats what the guy who gave it to me said.

Hopefully Dm93 can chime in and post the picture of the CPS and CKS wave forms like he did in another post.

 

This^^^ I really doubt it's a PCM issue but without having a scope on it rolling when the code sets there's no way to know.

This is all I have at the moment, it's from the FSM.
Essentially the crank reluctor is 35 -1 teeth so it generates 34 pulses per engine revolution, the cam sensor should generate 1 pulse every two engine revolutions or 68 pulses of the crank sensor.
I can look in the Pico library for a known good it I need to but if you don't have a scope it isn't gona do you any good.

 

The ECM is almost never the culprit of any given issue. Are you actually experiencing driving issues or is the code just annoying?

This code is thrown when cycles are being missed, which is usually due to a weak or failing sensor, but also could be grounding issues. You traced the ground path fully? Some have separated the cam ground from the crank ground for a cleaner signal.

 

I appreciate the input guys. No driving issues at all, just a recurring check engine light with a P0340 error code. The timing belt gear on the crank is new OEM as is the Cam Pos Sensor. This problem had just started before they were both changed out while doing routine mtx. No scope so I will have to have someone do it for me. But the big problem is that after clearing the code, I can drive for days before the check engine light comes on again. And the engine never misses a beat. Will keep looking and testing. I have an FSM on pdf. Thanks!

 

I mean I'd suspect a wiring or pin fitment issue before a PCM issue, I'd sure want to look at the signal with a scope although being that intermittent it may look fine until the fault happens but then again it could be something that may be visible on a scope even when the code isn't setting.
The code is a 2 trip code I believe so it may not turn on the engine light on the first failure.

 

With my luck, a single trip to a mechanic will not find this intermittent problem. A handheld scope might be in my near future.

 

Yea intermittents are always a pain, as someone that works in a shop I hate intermittent problems. Unless you happen to get lucky and catch it with your test equipment hooked up you may never find it but of course alot of the time when the customer comes to get it it acts up on them right away.
There's some relatively inexpensive single channel scopes out there but I can't say if they are any good or not as I've never tried any of them.

 

I am not very eager to bring this intermittent problem to a Toyota dealership. Historically, they have not proven to be much good at finding intermittent electrical problems in my Toyotas. It took Toyota 6 years to diagnose an intermittent O2 sensor on a then-new '96 2.2L Camry. Every time I brought it in, the result was always "Ops check OK!". The problem was only found when the O2 sensor completely failed in 2002. By that time, the catalytic converter had been destroyed by 6 years of erratic fuel burn which was a $1000 fix. I was a marine mechanic and have chased down my fair share of electrical gremlins, most caused by saltwater corrosion. But that was decades ago. I have not used on oscilloscope since I was in school in the '70s. Looking for a local shop that can scope the CPS signal at the ECU. Will change the female connectors to both the Cam and Crank Position Sensors. That is where I would expect to find this intermittent due to all the mud and water I have wheeled thru. They both look and test to be serviceable (Ohm test as per FSM), but that is the very nature of an intermittent. I carefully reinstalled the ECM after checking both ECM pins for the CPS and now can't get the Taco to throw an error code (of course!). So I am continuing with other routine mtx (UBJ replacement/UCA bushing inspection/brake system work) while waiting on the new 90980-10947 female connectors for the sensors. Just finished replacing the UBJs with OEMs and the UCA bushings are still GTG. Once this intermittent P0340 problem is solved, I will post what caused it. But being an intermittent problem, it might take a while. Thanks guys, I do appreciate all the help!

 

It definitely could be a pin fitment issue whether it naturally occured because of poor connector manufacturing or from someone jamming something in the terminal, I have to deal with those quite often. Sometimes you can visually see it other times a pin drag test finds it.

 

I just wanted to follow-up on the intermittent P0340 error code problem I was having which appeared to have been in the female connection (on front of the timing belt cover) to the new OEM Cam Position Sensor. The new OEM female Cam/Crank Position Sensor connections (90980-10947) were $7 each, I changed the cam connection out before Christmas, and have not thrown a P0340 error code since. Did not see any corrosion on the wiring or in the connectors but there must have been a problem with at least one connection. Am now calling this intermittent P0340 error code problem solved & I do appreciate the help!

OEM 90980-10947 female Cam Position Sensor connection appears to have been causing the intermittent P0340 error code:

 

Hello. Having the same issue with my 97. I am also getting P0300/01/02/03. It is not my daily so I do not drive it very often. Someone sold it to me with a bad engine. So put a refreshed one in it. I did get CPS code once with the old engine but I never really got into it. But I can get it to act up if am really getting into it hard. Did you have misfires as well? The guys that installed the engine said the old engine had that connector removed. They installed the connector off the new engine harness (butt connectors and shrink) and I used the new engine CPS so it still have its own connector. So I would guess it is safe to do this first. Wondering about the misfires though. Did you have any? Thank you bro.

 

I did not have any misfires at all, just a recurring P0340 code. Good luck getting your problem sorted out.