VETTLIFE

Considering this is such a common problem on our cars, including mine. I wanted to create a log of all the direct fixes and solutions to solve this issue.

Jump terminal A and G on ALDL connector located in driver footwell, turn ignition on.
Read codes on center LCD instrument cluster.

Module 1 - CCM Code 41 - Communication Error (CODE 41H History 41C Current)
Problem - Central Control Module (CCM) serial communication failure
The CCM requires constant encrypted data communication from the ECM at all times. The CCM communicates in a master-slave configuration, the CCM is assigned as the master and constantly polls injector and data from the ECM before startup in order for the vehicle to run and insure the VATS (Vehicle Anti-Theft System) hasn`t been bypassed. It also communicates with various other modules on the serial line reducing the number of wires required between modules.(early Canbus).

This is not to be confused with ECM error code E41 (Electronic Spark Control Circuit Open) when reading ECM codes. If ECM codes (module 4) come up ERR on the LCD cluster you can scan or jump the ECM directly from the diagnostics port A,B to pull codes directly from the Check Engine Light.

The C41, H41 CCM issue is mainly due to a defective ECM under the hood or open or short to ground of any of the CKT 800 (Tan) serial data communication wires and grounds between the CCM to ECM and other major computer modules behind the instrument panel. This problem can present itself on running and non-running cars depending on severity. A no start condition is typically the result from a complete ECM failure. The CCM shares serial wires and branches them from S222 behind the IP. An open or cut serial wire in the system will disable that specific module where a short will take out the entire chain.

HERE IS THE INSPECTION ORDER TO THESE TARGET AREAS AND SUCCESSFUL FIXES TO THIS ISSUE:
- Make sure AIR BAG fuse is OK and I/P to DERM harness connector isn’t disconnected under the passenger footwell. Look for large yellow wires. (Confirm with ECM code 51 which also causes this code) If so the ECM will not receive power and this code will set.
Also check CCM fuse 5% chance but easy to check.
- ECM replacement. Known to solve the problem around 35% of the time (Especially if the ECM has a broken mount and has been rattling around) Replacement ECM's can be found cheap by finding interchange info for other similar GM vehicles. Make sure you swap the EPROM chip into the new matching ECM prior to installing back in vehicle.
- CKT 800 (Tan) Wires and grounds or poor corroded connectors (Usually the problem 35% of the time)
- Faulty ignition control module, coils and failed linked computer components 17% (Will throw C41 codes as well)
- EPROM replacement, has solved the issue in very rare cases 5%
- CCM modules have a near perfect track record and have almost never needed replacement to solve this issue. The Factory Service Manual 8A Electrical Supplementation has a troubleshooting guide for the CCM to verify proper functionality prior to replacement. 3% (As a last resort after trying everything else)

Locations to check for faulty wires:
- Under the drivers knee panel (hush cover) Check C68 wire area for steering column or pedal linkage rubbing-pinched and exposing wires tan wires and coming from the ALDL connector itself.
- S222 Main CKT800 serial line main branch junction. Behind center of instrument panel behind HVAC unit. Very close to CCM. (Check for corrosion and clean)
- Physical wires leading to ECM (Especially if the ECM has a broken mount and has been rattling around)
- Wire junction area under the top of dash near right side of defrost vent up by windshield (can get corroded from moisture over time especially with existing heater cores leaks) Unfortunately this requires pulling the upper dash pad to clean and inspect junction wires and connectors.
ANY MORE TROUBLE AREAS YOU FIND LET ME KNOW

IMPORTANT TO NOTE:
ECM - Engine control module
PCM - Powertrain control module
ECU - Engine Control Unit
ARE ALL THE SAME THING AND NOT TO BE CONFUSED WITH THE CCM (CENTRAL CONTROL MODULE)

LAGATTU

Hi VETTELIFE,
I have a 93 LT 1 Corvette 180,000miles ,automatic box overauled ,throttle cable ,oil sensor (but not stiff ) ,.After box repaired ,I made tests ,and leaving home one minute after ,sudddenly ,rpm ,going up and down ,engine ready to stall , but I succeed to go back home .I was thinking short of fuel .....put some and drive 3 miles ,again rpm going uèp and dowm ,engine stumble ,and even with playing with pedal engine stall ,middle of the road ;As I have experience with opti problems ,I change opti ,with Petris ventilated ,,coil and ICM ,Before to install pump ,I try engine ,I had some difficulties ,but it starts ,and I try many times .Pump back ,firing test ok ,many times ,within a second ;So I want to see ,fans starting ,rpm ok less than 500 rpm ,engine steady ,fans starts something as 180° F ,evrything seams ok .and suddenly after about 20 minutes running , ,rpm going up and down gradually some misfiring ,and stall .Since then not any firing ,it cranks ,that all .I check codes ,after resets I have C12 ,H 16 ,H 72 .After again some checks as indicated by FSM , ,check codes now ,I have H 41 ,H 72 ;According to FSM ,as H 41 does not set ,going to diagnostics aids ,they say ,DTC 41 will be on ,if CKT 423 exceeds ,4.6 v ,and I got 11.9 v .
So I am completely losted ,and if ,you can tell me something about it ,will be pleased........

garwood94

My 1995 LT1 has a different issue - I tried to communicate with my PCM but get error messages every time (CATS Tuner, RT Tuner). Fuel pressure is great but electrical system is shutting the injectors down. PKE is not recognizing either key so I have bypassed the fuel pump relay which allows it to run for 5 seconds… During the 5 seconds, it revs and sounds great. I now know that my 5 seconds of run time is being controlled by the fuel injectors shutting down. I verified that I have constant fuel pressure to the rails, constant spark to the plugs, and still cannot communicate with the PCM…

esc493

I have a 93 we are having trouble tuning. Running leaner than should and power is way off. Pressure is good as is flow tried multiple injectors and confirmed power and ground. Noid light checked harness. My question is; can the ccm cause a lean issue in an injector pulse or timing? Any help is appreciated.

LAGATTU

Attention VETTELIFE ,
So today back on the job ,and here are my foundings .....With key ON ,B on ICM connections ,give 11,9 v, instead of 0,5 v. then I disconnect grey plug on ECM ,and look for continuity ,between A 12 ,via 423 ,line and Pin B the wire is open........same time I check on pin A 12 going out of ECM ,I have something as 0,1 ,0,2 v,which is good .Always with key on ,check ICM connections ,Pin A 0 v,Pin B 11,9 v, Pin C ground ,Pin D 0 v.So defects wtih Pin B ,Pin A ,Pin D,according to FSM .
For all followers ,I need your help ,to solve these problems ,,I think to install one outside wire ,from pin A12 ,up to ICM pin B ,and for no voltage to coil through A and D ,what do you think ? .Does I have to send my ECM to SIA ...........thanks for your replies

pcolt94

If you remove the connector from ICM for the measurements and measure on the connector. Pin A & D should measure 12 vdc. Voltage comes thru the coil which is supplied from the coil fuse 10A fuse 25.

Measurement of pin B is an AC measurement. This is performed using the AC scale on the meter while the engine is being turned over. Should measure about 4 VAC or a little less. A DC measurement is not made at this point because it is not referenced anywhere. But I would think it might read 5 vdc because it is a TTL (square wave) waveform.

Pin B is the drive for the ICM from the ECM/PCM. Without it there is no turn on for the coil or any spark.

LAGATTU

Hi pcolt94,
Thanks for your reply,;So on my ICM , I get ,pin A and D ,I have 11.8 volts;Pin C 0 ,and pin B while cranking on AC scale ,something as 0 ,v .As this control on pin B it's very important ,this afternoon ,I will check again ,because sometime ,when you are upset ,I make some little mistakes .........And if I find no voltage ,what do you advise me to do ......thanks in advance ........

VETTLIFE

I assume those errors are C41 and H41 from the CCM? If your passkey isn't working I would sort that out first or correctly bypass it behind the HVAC panel. Once the passkey system is out of the way you can rule it out.

VETTLIFE

You lean issue isn't likely from the CCM or injectors. If your not actually throwing code C41 or H41 then your issue is something else likely a sensor problem and not related to this thread.

VETTLIFE

I read somewhere some of the tan CKT800 wires ground to the tranny bell housing, check to see if you disturbed them while troubleshooting your transmission. Also If your OptiSpark is used or re-manufactured replace it with a new one, anything except CHINESE ACDELCO. Need to rule that out.

LAGATTU

Thanks VETTELIFE ,
Just to say what I have done already ,,due to a sort of misfiring while, driving ,(one time engine don't stall ,but second time stall on the road ) .So I change ,,opti with Petris ventilated ,AC new coil ,AC new ICM Before to assemble water pump ,,I had some problems to fire engine ,but I succeed ,,many stratings ,in a second ,as usual .Then place back water pump ,starts again many times ,and after I have ran up to fans starting ..RPM ,steady ,about 500 rpm ,and when fans started rpm going up and down ,some cylinders not firing ,then stall ,it was the same phenomena ,that the 2 times before .......since then not any firing .I pull codes out ,so (1) H 41 ,(4) H 16 (9),H 72 .,even after erasing codes ........
After checking with FSM ,on ICM A ,I had 11.8 v ..B 11.8 v ,C ground ,,D 11.8 v. So now ,I have repaired B problem ,because ther was a cut between A 12 ,through 423 .Now it's ok ,but I measure ,with DC scale ,will do with AC .after repair ,now I got ,with A and D ,0 .1 ,0.2 volts ........
Another thing ,checking all threads talking about codes ,not are saying same things.For H41 ,loss ECM ,data connection -ignition circuit open - ECM.....H 16 distributor ignition pulses,- ignition fuse 3 open .........H 72 VSS loss -radio out of service -LCD diming circuit .

If you have some ideas,of what ,I can go ahead ,it will be very nice ,for m,and thanks in advance .

LAGATTU

About ICM made country ,Mexico,and coil USA....

LAGATTU

Just to add to my last threads ,After various jobs ,and erasing codes ,now I got ,module 1 C 12 ,module 4 H 16 ,H 41 , module 9 nothing;But on ICM A and D ,not any volts ....and that worry me a lot ,as you can imagine .So again ,if you can indicate me some ideas ,they will be very welcome .

VETTLIFE

Your main problem isn't related to this thread, H41 means an existing intermittent communication problem which was likely a random event. If you don't have C41 your not experiencing this fault.

VETTLIFE

No, the CCM simply turns on the the fuel injector and starter relays after registering a valid passkey permission from the vats module. Furthermore the fuel pump is directly connected to ignition and has nothing to do with the CCM. Your problem sounds like a general sensor issue. The ECM and EPROM control injector pulse and timing however they are likely running lean due to erroneous data from a failing sensor.

VETTLIFE

Replacing my ECM solved my C41 and SYS error problem. Swapped my EPROM into the new ECM and everything is working correctly now. No more codes.

LAGATTU

Hi VETTELIFE ,
Back to works again .After a while ,with no works ,I check again ,about codes ,I got many times now ,same ,at ,C12,at 4 H16 and that's all......After all crank tests before ,I damage my starter ,,with a reconditionned one it's ok .Mean time I have sent my ECM to SAI electronics ,and everything back now ,still no start..Check opti hb

LAGATTU

Sorry wrong thing done by me ,So opti harness ,all checkings are ok as per specification ,ICM harness ,still A = 0 volt ,B ?? ,C = 0 ohm ,D = 0 volt.........I have checked on coli plug ,voltage from igntion ,I get 11.92 v .With this engine ,I replaced opti ,ICM , coil ,except that with these spare replacement ,I ran only 20 minutes.......and since ,not any starts .As opti ,don't receive not any signal from coil is it why I have H 16 ?? do you think I have to replace coil again .
Thanks for your reply .