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Autotech58, ASE Certified Technician
Category: Car
Satisfied Customers: 709
Experience:  38 years experience in the automotive repair industry with experience with many makes and models.
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isuzu rodeo s: 1999 isuzu rodeo..only code is p1627 a/d

Customer Question

1999 isuzu rodeo..only code is p1627 a/d conversion..the cooling fans constantly run..when i clear code the fans shut off till the engine light comes on..there is a problem with fuel sending unit..but i cut all wires from unit to computer and from computer to cluster..still trips and fans come on...any suggestions?
Submitted: 4 years ago.
Category: Car
Expert:  Autotech58 replied 4 years ago.

To understand why your problem still exists after cutting wires, you need to also understand that cutting wires CREATES circuit failures. The PCM is setting codes and turning the check engine light on to tell you that there is a circuit failure. Cutting the wires does not fix the circuit, but rather, ENSURES that the circuit cannot possibly work. The computer is still programmed to tell you that the circuit is not working....cutting the wires will not change that.


When certain circuit failures occur, the PCM is "smart enough" to know that it cannot "trust" the sensors that are supposed to be providing important inputs, so that it will know how to control things properly. So when these failures occur, the PCM is programmed to go into "fail-safe" mode. It will turn the fans on to protect the engine from potential overheating. Since it cannot trust input from it's sensors, it totally ignores them when it goes into fail-safe mode. So it does not know if the engine is really overheating or not and turns the fans on "just in case".


The correct "fix" for this is to repair all of the sensor circuits and/or the sensors themselves so that the circuits are functioning as designed. This is the ONLY way to make the computer happy.

Customer: replied 4 years ago.

i under stand..Have replaced pcm..temp relays..why is the code an a/d conversion..i understand limp mode..but i only cut the wires from the fuel level sensor to computer and from computer to dash.and it doesnt trip them codes..the only codes that this has had since its came to my shop was cam sensor and that p1627..replaced cam sensor and i didnt even have to clear that code it cleared itself when i started it..the only codes that has came back was this 1627..then i replaced the computer..(meanwhile gas gauge has been acting up the whole time with the gas light flashing even when it reads empty or full]and relays and temp sensor and check wiring......Im stumped

Expert:  Autotech58 replied 4 years ago.

To be honest, I do not have a really good answer for the P1627 thing, unless the PCM is the wrong PCM for the vehicle. According to the service information for that vehicle, that is not even a valid code. (See the diagram below, which shows a partial listing of possible codes for that vehicle.



Note that the code listings in the service information skip from P1625 to P1635.....


I also have no clue what you are referring to when you say "...the code is an a/d conversion.." unless that has something to do with trying to use a "generic" OBD scan tool to try and read "manufacturer-specific" codes. Any code that is listed as "P1xxx" is a "Manufacturer-Specific" code. These have no "set" definitions controlled by the SAE standards, and therefore, generic OBD scanners often cannot render the codes correctly.

The only other thing I know to tell you is to also keep in mind that the PCM shares information with the instrument cluster module. It HAS TO know the fuel level before it can control the EVAP the fuel level sensor circuit WILL affect PCM operation even though the fuel gauge circuits are not connected to the PCM itself.


You will probably have to scan the instrument cluster and repair any and all fault codes there, to keep the PCM happy - due to the fact that these modules share information via the data communications lines.

Customer: replied 4 years ago.

my snap on verus says p1627 pcm a/d malfunction

my mitchell say p 1627 is driver 1 input high voltage

and a/d is analog to digital..if i connect everything the fuel gauge acts up with light code for that..just the 1627..if i clear that code the fans shut off fuel gauge appears to work without light flashing then about 20 secs later engine light comes on fuel gauge messes up with light flashing with fans on high speed..only code once again is 1627...with new and old pretty safe to say that it is not the computer since they both do excact same thing..???

Expert:  Autotech58 replied 4 years ago.
OK hang tight....let me look that up in Mitchell and see if I can make any sense out of this code. I'll get back to you shortly.
Expert:  Autotech58 replied 4 years ago.

OK here is what I come up with....


AllData does not list that code at all (we already established that).

When I go to Mitchell, the code is not listed under the DTC Index when you click the link on the right side of the page. However, if I put P1627 into the "Search" in the center section, I come up with the same information that you provided.


So, apparently, Isuzu has not released diagnostic and/or repair information for this particular code to the is a "Manufacturer-Specific" code, so this does not surprise me....


However, I was able to go one step further:


I am a sponsor member of iATN and have the resources available from professional automotive technicians around the world.....When I checked their "known Fixes" database, I found several listings for this same code, with the same symptoms you are describing....Cooling fans that will not shut off and a fuel level gauge and light that is extremely erratic.


Although there was about 20 listings for this same issue, I only read through three of them before coming to this conclusion:


In all three of the listings that I read (I picked them at random), replacing the fuel level sending unit fixed the problem. So it would be safe at this point to assume that code P1627 IS for the fuel level sender circuits. Makes sense to me ANALOG sensor signal that must be converted to DIGITAL in order to share among different modules.


So at this point, I can only refer you back to my original post where I stated:


"The correct "fix" for this is to repair all of the sensor circuits and/or the sensors themselves so that the circuits are functioning as designed. This is the ONLY way to make the computer happy."


Repair the fuel level sensor circuits.


Let me know if I can do anything else for you.

Customer: replied 4 years ago.

i want my money what ur tech sent me..i answered the question before he did...he shoulda told me that the fuel level sensor was related to that code...he didnt say that till i told him..and i found it threw the internet..ty john..3308120177

Expert:  Autotech58 replied 4 years ago.

Umm....Pardon me???


You NEVER told me that this code was for your fuel level sensor circuits. In fact, you spent your time on this post DENYING that the code in question had anything to do with the fuel level sensor circuits. You continued to INSIST that this code was NOT due to a fuel level sensor problem, even after I had told you not once, but TWICE that you needed to repair these circuits.....the first time being in my ORIGINAL post.


"..i understand limp mode..but i only cut the wires from the fuel level sensor to computer and from computer to dash.and it doesnt trip them codes.."


"..if i connect everything the fuel gauge acts up with light code for that..just the 1627.."



You might try to remember what you said, or even better, "re-read" this thread yourself before making such non-factual and totally unmerited claims, in an effort to avoid having to pay for the services that have been delivered in good faith on your behalf .


It would probably be much better for both of us to stick to the facts as they appear on the page. Please keep in mind that anyone else reading this thread can read the ENTIRE conversation in its full context....


Just as a customer is not automatically relieved of having to pay for diagnostic time in an auto repair shop because a similar diagnosis is also available at a different shop location, neither should a customer be not held accountable for paying for the information asked for, and subsequently provided for him, on a pay web site, simply because similar information may also be available on a different web site.

Yes, you probably will get your refund if you take this up with customer service and insist on it. However, you should also consider that unlike most of the open forums around the internet, PERSONAL INTEGRITY can go a long way on this web site. You just might need some professional assistance again in the future. I do not believe your latest actions here would be very beneficial in helping you get it.


....just in case you would like to "re-think" this one.....