Hi , I have a 91 Eldorado,about 3 weeks ago I tried to start it at work(night time) all lights came on headlights looked bright but when I went to crank it nothing happened (all dash lights good) and DIC said 'SYSTEM PROBLEM' checked codes and B334 was current , later looked up means communication fault between ccdic and ECM. Well anyway that night I got someone to Jump the battery and it started drove it home, cleaned battery terminals. The car ran fine everyday for 3 weeks after that then at work again when leaving again NOTHING errcode B334 and could not get car to start, got a ride home and next day went in and it started no problem drove it home. Replaced starter drove it another day got home this time and now the car will not start at all same b334 error. (Wife has same year model car) so put her ECM in my car still will now start, mine in hers started her car. I have service manual and grounded wire as it says and temp portion of DIC goes blank supposed to mean bad ecm?? but it aint... another note last few times after problem and car did start I heard a BUZZ sound from dash when ignition to START, but subsequent start no buzz, so can't trace source of buzz though it sounds like a relay. Right now CAR is DEAD , which should make it easier to troubleshoot though I am not sure what to try next. With key in RUN I hear relays for RAP and FUEL kick on but ingnition to start I get NOTHING no sound (lights/dash all good) just 'system problem' message on DIC. Any help would be appreciated thanks John

Are you getting any of the PASS-key warning displays at the climate controll center?

No not getting passkey , had that before in wifes car , does not count down, when I put key in all looks good (normal) then after monitor systems message it says 'system problem' I can read codes (no ecm) and only get B334 from bcm. But reading service manual seems No ecm code is because this errcode is for communication fault ecm to ccdic

Ignition switch?

Hi all, I found the problem. Since service manual pointed to ECM or memcal,and replacement did not fix, I looked into where the power to ECM comes from. Checking voltage at ECM only had 6.7volts, so traced back to Battery and the ECM is fed by a FUSIBLE LINK whicj splits off to PASSKEY and ECM, I hace 12 volts before link and approx 6 volts after?? removed link and spliced wires together and now starts, removed and same fail condition. I installed a max fuse (all links I can find are TOO thick a gauge) and manual says use same gauge wire for the link. I installed a 7.5 amp fuse start. Is there a way of knowing how many amp fuse to put in. the wires for this circuit are thin compared to other fusible links. this link has 1 wire from BATT and split to 2 after link one side feeds ECM 2nd feeds passkey thanks John