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module 4 data missing when accessing vehicle codes via OBDII/OBDI...?

 
chunkyjaa
I love my Chevy Chevette!
Posts: 9
Joined: 09/13
Posted: 09/06/13 03:03 PM

Have a '95 LT-1. Starts smooth, runs OK , but develops mid speed miss. Idle starts to stumble, the SYS light, engine smooths out, fans kick on (everytime). Access veh codes by comnnenctig pin 4 to 12, get code 12 (It's Ok here_ then module 1, 7, 9, and a, All with ---. No module 4 is ever displayed. An obdII scanner won't talk to the car . Anyone ever see this. I'm trying to see why a sys light is lit, and suspect it's PCM related but no module 4 . Any help with be greatly appreciated  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/06/13 05:48 PM

not all OBD2 scanners will talk to an OBD1.5 car.. sorry..94 and 95s are PAINS in the seating areas if you don't have the proper diagnostic tool...

does your 95 have the C68 fully automatic A/C???

if so.. turn key on.. on the climate control head.. find the OFF button and the warmer.. it might be the right side UP arrow...   hold off and warmer on until dash lights all light up.. then release... if this works the way i think it does..  you should be able to find a display thats flashing codes..   please.. do not have the engine running only the key on.. and without your foot on the brake..

you could have several issues...

a cheep thing to change first is the engine coolant temp sensor along with the pig tail connection.. SU102 is the part number for the kit at autozone..  or from wells   under 20 bucks..

when the fans kick on.. this is kinda indicating that the engine coolant temp sensor or pigtail has failed..  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/06/13 05:53 PM

you also might want to go over the ground connections..

94 C4 LT1 Enginediagram Zps6ddaef03

94 C Lt1batterycables Zps57ba2834

you will want to also run the second half of this test..

Voltagedroptesting  

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chunkyjaa
I love my Chevy Chevette!
Posts: 9
Joined: 09/13
Posted: 09/07/13 06:04 AM

Thanks, I changed both sensors, the one on the water pump and the one in the head, . However the temps are 15-20 degrees apart between the digital and analog. I will do the pump pigtail anyway. How close should they be? thanks for your direction  Ed  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/07/13 06:47 AM

20 degrees off.. but the sensor and pigtail in the water pump control only the fuel injection should have 2 wires...  

the sender in the head is for the gauge.. has a single green wire probably..

and please at least spend the 5 minutes to run the voltage drop test..

why.... if you have more than 0.02 volts.. 2/100ths of a volt on test #4...  you will have an incorrect reading on the dash display... as the TEMP SENDER... is only ONE side of the circuit.. the other side is the ground..

and the ground side carries the charging current from the alternator case... the high voltage spark return path..  what.. the spark does not just end at the cylinder head...

i run that test on almost every car i work on as it comes in.. and on every one before i close the hood and return it to the owner...

i found a 98 chevy pickup one day.. that just ran horrible.. and it liked to blow alternators.. gauges all over the place..

it had 8.5 volts on test 4... between the engine block and the body..

test 2 and 3 were both over 1.0 volts..  but test 4 at 8.5 volts blew me away...  i cleaned the various ground contacts and that truck ran for another 6 months .. till the owner ran it low on oil and then complained about the engine making noises and a big bang and fire under the truck.. i have a picture of the hole in the side of the oil pan if you would like to see it...  

he just bought a replacement truck... a 96 4x4... it had the same issues.. the ground connection at the front passenger side of the block was soaked in grease and covered in road dust.. it had 1.4 volts on test 4...  and between the alternator output stud the positive battery terminal there was over 1.0 volts also.. i think it was closer to 2.. the nut on the back of the alternator was actually loose.. it was just snug.  not tight enough to really be properly effective...

someday.. he will let me put a motor in that 98 C2500 .. it only has 290K miles on it.. so its just barely broken in..  

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chunkyjaa
I love my Chevy Chevette!
Posts: 9
Joined: 09/13
Posted: 09/07/13 02:56 PM

Will do tomorrow. Your help is really appreciated  

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chunkyjaa
I love my Chevy Chevette!
Posts: 9
Joined: 09/13
Posted: 09/08/13 04:40 PM

Pulled the battery, cleaned the + to both fuse panels, cleaned and reterminated both grounds on the frame rail beind the batt. With a jack and stands could not get to the points above oil filter and bell housing. Tests are all within range. Ran the pin 4to 12 test again, disdisplays only module 1,9 and a. Went for a fast drive, different stuff, sys light comes on an and off more often, more rough running than before. Just for giggles hooking # 4 cable between - and block. I.m becoming more convinced that I,be got a ecm problem. BTW, the procedure to pull codes via the A/C bottoms did not work.
Added #4 grd lead from Batt to block. Car ran great for 2 hours. Gauges were more responsive, could tell the difference, No missing. Then started to miss, Sys light still comes on with the fan. Still get no module 4... Tired of chase today  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 02:57 PM

running an additional ground from the battery to the block... made it work better...

that really indicates there might be a ground issue...

each of the different ground wires.. actually connects to a different circuit...

i don't know what it's going to take to get into those ground connections. above the oil filter .. and also on the bell housing to engine block bolt/stud..

another forum member did this on his 89.. and it was a REAL pain.. he actually found the negative cable actually LOOSE at the back of the bell housing as i recall..

why are the grounds important..

let try something else..  do you think it will work well.. if the negative battery terminal was loose??

covered in corrosion..  just sort of wobbling on the bolt..   same effect farther down..

electrons flow from Negative to positive..  if you don't have both sides hooked up properly.. you won't have enough electrons to operate the circuit.. since your car is like 19 years old.. its time to clean the grounds..

if you got into the computer and checked the various ground wires at the computer to the negative battery post with a voltage drop test.. you would see which ones are acting up...

i had a nissan 300ZX for a trouble shooting job.. i measured the oxygen sensor voltage.. it was like 1.26 volts...  when the sensor can create under normal positions 0.1 to 0.9 volts.. and it won't create 1.26 volts.. at least that model won't.. it was a 3 wire heated oxygen sensor just like is on your car..  i went looking for the ground wire connection..  found the one for the throttle position sensor and one other item and i put a jumper on that to ground.. ..  but could not find the oxygen sensor ground..    got my mirror.. nothing..  i went and found the 500 page factory service manual.. on the last page of 100 pages of wiring diagrams.. it showed the ground location for the oxygen sensor.. when i went back behind the head.. i noticed that there was tape on the harness..over the factory tape.. when i unwrapped that tape.. i found the pair of ring terminals i was looking for..  when i hooked that pair of ring terminals up.. and removed my jumper.. the car came back to life..                  ran smooth.. a few more repairs and it passed smog...   i saw that customer later as he sped by... he was crazy happy.. it had never run that good ever...

do you have a set of wiring diagrams..??? or better.. a factory service manual for that exact year..

or online data ?????

i love my ball end extensions... so the socket can wobble off angle slightly..  

                                                         





################



i am taking you have the C68 climate control...

perhaps corvette uses a slightly different set of commands than the similar system in the caddys...

96 C4 Enteringdiagnositcs Zps3435cf40

i don't have a book that covers the 95 units.. i have a big 97 that covers all domestics..  but i don't know if its different..

i usually push the ^ arrow button .. second from the right.. top row and the OFF button. all the way to the left on the bottom row .. holding them down for 5 seconds..  with the key on.. your foot NOT on the brake..


are you in the los angeles area.. if so.. i have 5 scan tools.. i should be able to drag a code out of it..  3 of them handle OBD2.. and might cover obd 1.5..

i just cannot afford the access to all the professional info online.. its a LOT of money each month and i do this for free.. in my spare time..

i understand how it works and how to diagnose most of the engine controls.. i just use my scan tools instead of dashboard diagnostics...  i do those on caddy.. but its complicated...

let me see what i can find for the 95 models.. unless you either have a printed factory service manual.. one on CD/DVD.. or  have access online to either eautorepair dot net or alldatadiy dot com..  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 03:04 PM

The 94 and 95 Vette's have an OBDII Diagnostic connector but are not OBDII compliant.

To enter diagnostic mode.
Short pin 12 to pin 4 or 5.

Turn ignition on. Do not start the engine.

Connector located above driver side right knee and pin out looks like below.

01,02,03,04,05,06,07,08
09,10,11,12,13,14,15,16

After turning the ignition on the CCM will display
any Diagnostic Trouble Codes (DTC's) and the module for which they apply in an automatic sequence.

CCM=Module 1
PCM=Module 4
ABS/TCS EBTCM is Module 9
DERM (Airbag) is Module A

Each DTC is displayed for 3 seconds followed by a one second pause before the next DTC is displayed.

There is a three second pause between the DTC display sequence for each module.

The end of the DTC list for each module is indicated by
"----" being displayed in the speedometer.

If there is a communications problem between the CCM and the other modules, "Err" is displayed.

The particular module being interrogated is indicated on the trip monitor, and the DTC's are displayed in the speedometer.


CCM DTC C12 is a good sign. It means, On-Board Diagnostics are Operational, and there are no DTC's
(Diagnostic trouble codes) for the CCM (Central Control Module).

For the CCM module, C means the DTC is current.
H means the DTC is no longer present.

For the other modules, the error codes are always displayed as a H (history) code whether they are current or history.

There are some useful things you can do when in diag. mode. An example would be to clear any codes in the CCM or PCM(Powertrain Control Module).

Example to clear CCM error codes.

Ground pin 12 to pin 4 or 5. Turn ignition on and let the display cycle till it completes.

Press Trip/ODO button on the DIC until 1.7 appears in the trip monitor area of the cluster.

Press ENG/MET button on the DIC and hold until "---"
appears in the speedometer area. This will any CCM DTC's.

Turn ignition off then back on and verify no DTC's are present.

To clear any DTC's for the PCM you would do the same thing but use 4.7 instead of 1.7.

When in diag. mode the CCM can also be used to energize different relays such as the Courtesy lamp relay, horn relay, rear defogger relay etc...

The CCM can also display the status of the items that it monitors, such as seat belt switch, high beam
switch, low oil switch, fuel level, Ambient light sensor,
Ignition voltage etc...

So the diagnostics can provide valuable information if you need to trouble shoot a circuit.
 

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chunkyjaa
I love my Chevy Chevette!
Posts: 9
Joined: 09/13
Posted: 09/09/13 03:20 PM

I'll try again see what I get. I'm near tampa, but thank you for the kind offer.Let you know  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 03:58 PM

go back and reread my last 2 posts.. i edited the upper one ..


i think that you are getting exactly what you should..

in the modules only.. if there are no codes stored.. according to what i read...  you won't get info for them..

ground issues won't set a code... as the computer or device is just kinda UNPLUGGED from the wall..

it does not know its supposed to be ON.. because there is intermittent power...  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 04:08 PM

by the way....

exactly what brand and model scan tool do you have.. so i can look up an owners manual for my end..

i have OTC monitor extended versions that are about 12 years old.. they are obd1 and obd2... and i a have a bunch of cartridges..

i also have something cheep but it does the job.. a harbor freight 98614 scan tool..  they have a newer version at harbor freight stores...

this is the current version
Image 22526
CAN & OBD II Scan Tool With ABS Item #60794

i have not tried the more expensive version there..

i know the less expensive versions there only read codes and display snap shot data...

you need live data stream.. and the ability to graph the data stream...

graph.. yea.. look at the oxygen sensor voltage swings when held at almost stable 2500 RPMS..

O2B2S1 Zps69fd0fbd  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 04:55 PM

in one of the actual corvette books i have..
the LT1 has grounds on circuits

150
151
250
450
851

i don't have a ground connection locator...  thats why i cobbled the diagram way up for you...

i am taking you have a digital volt meter.... lets run a few more voltage drop tests...

engine running.. headlights on... digital volt meter set to 20 volts DC...   one test probe attached to the negative battery post...

the other probing the 16 pin connector #4.. thats circuit 150..
should be less than 0.04 volts... this is a black wire only.. no stripe.

then move to the next pin .. #5 thats circuit 851..
this is black and a white stripe wire.
from the PCM connector pins..  

A2,
A18,
C32,
D1,
those all seem to be grounded to the block.. and should read like above less than 0.04 volts dc... these last 4 are black with a white stripe...  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 05:04 PM

hmm....this is the body version of the diagram you need...
it does not show the locations for any of the numbers above..

150, 151, 250, 450, 851..

C4groundlocationsbetter Zps1ad2340d  

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waynep712222
My first time was in a Chevy
Posts: 129
Joined: 03/13
Posted: 09/09/13 06:09 PM

i did some more digging...

get to the front of the motor.. there are several wires on the ignition coil mounting bracket...

count them..   take them off.. take the bracket off.. take the stud out..    wire brush everything that will improve your grounds..

Optisparkg111 Zpse3397a4f


there is another ground location down near the right hand oxygen sensor connector.. in the same harness that feeds the connects to the starter motor..

take that off the block and clean.. then reinstall it..

i cannot guarantee.. that this is all the ground locations.. but it might be for the engine control wiring harness..

now.. you talked about issues when the fans come on.. this are the fans with the C60 manual climate control for the F body.. but it will give you an idea.. your car probably uses the lower 3 relay control.. but i cannot tell from here...

LT1 Fbodycoolingfans Zpse13442ff

95LT1PCM1 Zpsf469d2b7

Optisparkwiringdiagram Zps7ddc6988

now... this is the wrong motor... starter on the Wrong side.. but it is what i expect you to find on the bell housing bolts / studs to need to take apart and clean... this is battery to engine connections...

Groundsbystarter Zps0f36176e  

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