New member here. First let me say thank you as I have spent the last month "lurking" and taking advantage of the useful information contained within these walls. I am not a mechanic by trade so hopefully this description is thorough enough to explain my issue at this point.

Heres the technical info:

2000 Honda Accord EX AT 2.3 L4 VTEC SOHC (F23A1) Sedan

P1259 - VTEC Malfunction
P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

I should have the new O2 sensor by lunch today so hopefully that will clear that code


My wife's original engine had 189,700mi when we completely lost compression in the #4 cylinder. I ordered another A1 and performed the swap about a week ago. All in all it was pretty straightforward and went in with little headache. At first I had some surging issues which were a combination of swapped cables at the intake and a filthy IACV. Once that was corrected I noticed that the car would idle smooth as glass but when I attempted to drive the vehicle it would hit a "rev limiter" around 4,000RPMS. More searching showed this was a result of the ECU reading a P1259 and putting the car in "limp mode" which I can only assume will protect the car on its ride back to the dealership.

I began searching forums and came across this site. While searching "VTEC or 1259" I have tried a few different fixes only to still have the issue.

*Changed the oil and ensured it is full
*Taken the VTEC spool assembly apart and cleaned the screen/filter
*Tested continuity between the lock-up solenoid base and body-ground / negative terminal (Haynes Manual)
*Tested for 12v on solenoid harness with switch in on position (Haynes Manual)
*Test continuity across the two contacts on the oil pressure switch (Haynes Manual)

Last night when I made sure the oil was full I cleared the code and the car was able to rev past the 4k mark. I took it for a drive and it drove like a dream. After I slowed down and did a u-turn to head back home I took off, not too aggressive but enough to pull out into a 70mph zone and as soon as I hit the 4k mark it started to shutter again. I had the scanner in the car at the time and it had 1259 displayed on the screen. Once I cleared the code I was good for about 15-20 seconds until it threw the code again.

So I feel at this point I know what the issue is but until I fix the part in question it will continue to place the car in limp mode. I feel like I've checked all connections and I am losing my mind at this point. I have learned a lot about this car during these last couple weeks and I would really like to solve the actual problem vs just changing the whole unit, unless it needs to be done of course.

With all of that being said do you guys feel its the solenoid, oil-pressure switch or entire assembly at this point? Thanks for any advice you can give me!

 

P1259 is an electrical fault in oil pressure switch circuit, or VTEC solenoid circuit.

Fault appears to be a "hard" fault that is always present, and if external to ECM it should be detectable. It could be 1) faulty oil pressure switch, faulty solenoid coil, faulty connector/s, faulty wiring on either circuit, or faulty ECM.

Engine replacement offers lots of opportunity to damage wiring. I damaged my vtec control solenoid single wire connector due to repeated distributor removals which required removing that connector. This is a case where Obd1 was better than obd2, as there are separate codes for VTEC solenoid (21) and vtec pressure switch (22).

Suggest confirming wiring/connectors/switches/solenoid coil at the ECM/Harness connection. If all checks good from this position, the ECM is likely source of the problem.

good luck

 

Is it possible to mix up the electrical connectors for the components at issue?

 

Unlikely, one is a dual pin and other is a single pin. Also appears one is oval and other is circular, but this is not entirely clear in pic.

good luck

 

Take a long hard look at your oil pan. If it's dented it could be causing your issue since vtec requires a lower threshold of oil pressure than the oil pressure switch and a dented oil pan causes a loss of oil pressure at times.

 

Resolved.

I took the groups advice and began checking connections. I noticed every time I would turn the key to the II position the cooling fans would come on. I didn't think this was normal because while fixing another issue my Haynes manual said to hold gas to 3k until fans come on....

So with the key in the on position I would connect / disconnect the harness going to the VTEC and the fans would go on/off. I looked at the harness going to the thermostat housing and wouldn't you know there was an identical connector, green in color and it seemed like it was stretched way too tight. I swapped connections and the fans went off.

Started the car, cleared the code and she is now running like a dream. I feel awful for not catching that earlier and can only attribute it to a combination of beer and tools.

Thank you all and i'll edit this post in the future with pics and troubleshooting steps to assist others who may find it.



To all that may find this thread in the future my problem was with these two harnesses being swapped. They are shown correct in this picture. If you turn the car into the on position and your fans come on immediately, you have the connectors swapped at the VTEC assembly and the thermostat housing. Here are some steps to follow when troubleshooting a P1259 VTEC MALFUNCTION code

*Check your oil before anything else (some have also mentioned check for dents in your oil pan). If low; fill oil, clear code and retest.

*Verify ALL connections in that area. While the VTEC solenoid and oil pressure switch cannot be switched, the coolant temp sensor has the same connector and is in the same location. The correct connector will have a blue/black wire. If your fans are coming on as soon as you turn the car on, they are backwards

*Test for continuity between the base of the lockup solenoid and body ground / negative terminal.

*Test for continuity between the two pins on the VTEC spool assembly oil pressure switch. Should have continuity, if not replace

*Disconnect the harness going to the VTEC lockup solenoid. There is only one pin as the ground is supplied via the base. Use a FUSED jumper between your + battery terminal and the solenoid. You should hear the solenoid click every time you touch the +battery post. (key needs to be in the II position but not running)