Hello all - the home projects have had my spare time all filled up this year but I need some help diagnosing a VTEC/VTC issue.

2006 4 cylinder with auto trans - I don’t have my notes at the moment but I’ll post the engine number tomorrow as well as confirm the mileage - I’m pretty sure it’s over 175,000 miles.

I’ve been looking at this on and off for the past year - my boss bought it to use as a loaner for customers and we just need to get it figured out so we can start using it.

Codes P2646 & P2647 were set originally. The issue is it acts like it’s trying to engage the variable timing system at 2600 RPM, but it immediately disengages, causing a “surge then cutting out” symptom up to about 2800 RPM which will continue as long as you keep the gas pedal down.

The same codes continue to set but not at the same time - sometimes it’s P2646 and sometimes it’s P2647 - I’m yet to determine what operating conditions make the difference.

If you accelerate really slow and easy and keep the RPM below the variable timing threshold, the car drives just fine; but even under light/normal acceleration if it hits 2600 RPM, the surge is there.

I try to be very thorough in my diagnosis by verifying all related wiring is in tact and the correct voltages/signals are present.

That said, I make plenty of mistakes.

Here’s the list of what I’ve done so far (not necessarily in this order).

Changed oil to weight on cap (can’t recall what it is at the moment).

Parts Replaced:

Rocker arm solenoid and switch assembly (Dorman) and connectors due to corrosion.

VTC filter screen due to degraded/cracking rubber. Screen was clean with little accumulation of metal or debris.

VTC oil control valve and connector due to corrosion.

Due to the corrosion found in the first few connectors, Inspected the connectors for the cam and crank sensors as well as other primary engine control components. No problems found that I can recall at the moment. Also Inspected grounds/ground straps and cleaned or repaired as necessary.

Tests:

Performed air pressure test on rocker arm assembly using air regulated to 42 PSI per service manual. Every locking pin on the rocker arm assembly engaged/disengaged correctly.

Checked oil pressure at the rocker arm switch port - can’t recall exact numbers but it was above 50 PSI at idle. I may check this again to verify.

Verified the rocker arm switch turns on (or off? …. let’s say changes state ) when the solenoid is energized.

I also blew compressed air through the oil passages I could access when I was replacing the solenoids, filters and performing the air pressure test. No indication of debris accumulation.

I’m not sure what else to look at other than going back to the beginning and starting over.

Also, it’s not clear to me from reading the service manual - are the VTC/VTEC systems active at the same time, or are they activated at different times depending on engine speed and load?

Thanks for reading my novella and giving your feedback.

 

Are you getting the same codes after your repairs to the system?

How are you testing voltages? Volt meter or test light? Are you back-probing the connector or are you unplugging the connector and testing the pins?

 

I should have clarified - yes the same codes continue to set after the repairs I’ve done.

My test methods and tools vary depending on what I want to know. I use a Fluke 87, incandescent test light and an Autel MS908 to monitor live data.

More engine info -

Code is K24A8
Mileage is 143,500 (not sure why I thought it was over 175 other than my brain f***king with me)

Question about the rocker pressure switch -

As I’m understanding it, the switch is to remain open when there’s no oil pressure (solenoid off) and should close when there is oil pressure (solenoid on), correct?

The data stream reads both the solenoid and switch in ON/OFF states.

This was probably something I overlooked before (like I said, I make plenty of mistakes ) but as I was basically starting over in my diagnosis, I noticed in the live data feed that the oil pressure switch was reading ON at idle and switched to OFF at about 1500 RPM.

The solenoid was being commanded OFF the entire time.

If the PCM is expecting the switch to change states in parallel with the solenoid (both ON or both OFF), I suspect the replacement solenoid assembly may be faulty or there could be a short in the control circuit that’s causing the solenoid to remain open even if it’s not being commanded on.

So is it correct that there should be absolutely no oil flow through the solenoid if it’s off, or is there a limited amount of oil flow to provide lubrication to the cam and rockers?

If there is a limited amount of flow, what pressures should I expect to see?

Thanks again.

 

The shop manual says that the blu/blk wire at the oil pressure switch signal should be 0V at low rpm and battery voltage at high rpm. Can your scanner show voltages on the sensor?

What are the 2 wire colors on the vtec oil pressure switch?

 

Wire colors are blue/black and brown/yellow.

I’ll have to look again to see if it reads the voltage, but even if it doesn’t, I can back probe the connector and see what it’s reading.

Thank you.

 

Well, as many of us are aware, a new part does not mean it’s a good part.

Turns out the Dorman solenoid assembly was faulty.

I had to “reset” myself on this and approach the problem as if I’d never seen this car before to pull myself out of the “but I already did that” mentality.

I put my mechanical oil pressure gauge in place of the rocker switch. At idle, it was reading about 15 PSI. As I increased the engine speed (in park) it continued to climb, hitting about 80 PSI at 2600 RPM and peaking at about 90 PSI as the engine surged.

I verified it wasn’t a short to voltage by just unplugging the solenoid and got the same results. Then I verified the control circuit for the solenoid by using my test light as the load and watched the voltage and PCM live data as I grounded it - KOEO, it read about 3.5 volts and pulled down almost to zero and the PCM recognized the change of state.

I then did the same check on the switch circuit, only I pulled it straight to ground and got the same result.

I replaced it with an SMP solenoid assembly, cleared the codes and test drove it - no problems at all.

I’ll try to get some diagrams posted later to provide a better visual of the tests I did.

Thanks for the help.

 

I'm glad you figured it out. Dorman parts seem to be hit and miss on failures out of the box.