Nissan Frontier 1998 manual trans and 2.4 liter has a high idle and no comms

My Frontier has no communication with either diagnostic port (16 pin port or the Nissan Consultant port) so no scanner works (I tried several scanners).  I replaced a 7.5 A fuse that had been blown and that feeds 12 V to the 16 pin diagnostic port.  My symptom is a high idle (1,500 rpm at all times).  It began to have a high idle after running fine for years.  When I start the truck, I now hear multiple clicks from a blue solenoid under the dash, then the truck idles high all the time.  I tried replacing the blue solenoid with no improvement.  There is very little power when driving now.  I replaced the inlet air control IAC valve with no improvement.  I replaced vacuum lines and looked for vacuum leaks with no leaks found yet.  Do you think the throttle position sensors could be causing this condition?  I have various scanners that can be remote onto (Autel BT609 that is about 3 years old, a Topdon Pheonix Plus that is new).  Marty 850/597-1316.

Marti is fuse 11 good? maybe try to get ob connector fixed first to help you . I think you got map sensor and soldnoid on that truck check both also a miss fire will give high idle i think with map . good luck

Did replacing that fuse restore communication with the scan tool?
Is there now power on pin 16?
I'm with Lupe, I would probably go after the no com first to gain some direction.

Yes there is now power on the 16 pin OBD port and the two grounds are there but no communication with any scanner. I'll attach a wiring diagram of this system in my next message, about 6 PM today. Thanks

I will check the manifold air pressure (MAP) sensor and wires today after 6 pm. What do you mean by solenoid in your reply? Quote: "map sensor and soldnoid." Is that the idle air control (IAC) solenoid you are referring to? I replaced that with no reduction in idle speed.

Im just wondering if I am able to post wiring diagrams that I have from my subscription to Automotive Electricians Portal? I don't know if there is a prohibition on posting materials that I have a subscription to, but I guess not...

There has been no issue posting diagrams here on the forum.

Here is the wiring diagram from automotive electricians portal

Yes, fuse 11 is 12 volts on each side so it's good. I looked at the MAP sensor and solenoid and there is 12 v on one wire and 0 volts (a ground?) on the other wire. When I unplugged it the truck ran very poorly, so I think it is functioning to some degree. Is there a resistance measurement I need to make on it? thanks

I've checked the MAP sensor solenoid and it clicks when KOEO. I then checked the absolute barometric pressure sensor which shares a vacuum hose with the previous sensor/solenoid. It shows a good ground. Next I'll back probe the sensor line and apply a vacuum and see if the volts on the signal wire drop under vacuum..

Also, fuse 7 has no power on either side of the fuse, either with KOEO or with engine on.

Any suggestion on getting communication on either the OBD2 or Nissan Consult connector for diagnostics? Do I look for resistance with all the power off? Which pins do I check ohms, and which of the 2 diagnostic ports...

Marti wrote:

Yes there is now power on the 16 pin OBD port and the two grounds are there but no communication with any scanner. I'll attach a wiring diagram of this system in my next message, about 6 PM today. Thanks

How about the K-Line on the 16 pins connector (OBD2)? If you have a breakout box, you could  connect the scanner on the obd2 port and see if you have activity on pin 7 at the box when you are attempting to communicate. Since the truck runs, most likely the resistors are fine. If you want to check them, ohm pin 6 and 14. 60 ohms is ideal.
 

Marti wrote:

Any suggestion on getting communication on either the OBD2 or Nissan Consult connector for diagnostics? Do I look for resistance with all the power off? Which pins do I check ohms, and which of the 2 diagnostic ports...

There is not much to the communication with the ECM via the OBD2 DLC.

First, make sure that you have good battery voltage on Pin #16, and good grounds on Pins #4 and #5 of the DLC.

Next, as Monde suggested, check for voltage activity on Pin #7.

The K-line (pin #7) should have 12 volts when there is no network activity,  and toggle to ground with communication.

That's all there is to it. If you find you have nothing on Pin #7, you need to go to the ECM, Pin #69, and check there.

 
 

This is good information, I will check for 12 v on the K line and provide an update.

With key on engine off (KOEO) there is 7.7 volts on the K line (pin 7). It goes to about 9 volts with engine on. Pin 16 shows 12 v with KOEO and 14 volts with engine on. The two can lines 6 and 14 show no continuity with the ohm meter connected between these pins. What's the next test?

I did not have the scanner on and trying to communicate when I tested the pin 7 of the OBDII connector. Should I try to put an oscilloscope on pin 7 and try to communicate?

Do that and see if the voltage drops as the scanner tries to communicate.

With key on engine off (KOEO) there is 7.7 volts on the K line (pin 7).

 A quiet, idle K-line should have 12 volts. If you are using a volt meter, and there is something that is trying to communicate, such as a "babbling node",  you could be reading the average of a square-wave.

Should I try to put an oscilloscope on pin 7 and try to communicate?

Yes. That will answer the question of whether you have low voltage on the K-line or, if there is something trying to communicate.

The two can lines 6 and 14 show no continuity with the ohm meter connected between these pins.

This vehicle does not use CAN. Pins 6 and 14 are not used.




 

im having trouble with posting to the forum. I don't know what my user ID is so I am unable to send a request to support.