Engine: FI and Ignition Computers                                                               FAQ Home
Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
Bad ECU Diagnosed

Engine Failure/No Start: Bad ECU  [Link]

Intermittent Stalling; Bad LH 2.4 ECU

Buying a Used ECU

Buying a Remanufactured ECU

760T Engine Stops Dead at 60MPH; Bad Ignition Module

Bad ECU Diagnosed. [Suggestions:] has the mechanic checked all the inputs to the ECU at its connector? All grounds, power and sensor inputs should be tested at this plug before the ECU is condemned. Is the ECU is getting a signal from the ignition system? How about power from the ignition? I take it for granted he has checked the fuel pump and injection system relays.
[Response 2: Richard Keys]  The common cause for ECU failure is due to excessively high stray high voltage levels within the engine compartment or by unusual signals being seen by the ECU`s sensor inputs.  If this situation occurs, then it is strongly recommended to replace the high voltage system with new genuine parts (i.e spark plug leads, distributor cap, rotor, coil) and the main engine to body and battery grounds are renewed before fitting a replacement engine management ECU.

See also Engine Failure/No Start: Bad ECU

Intermittent Stalling; Bad LH 2.4 ECU. [Symptom: Intermittent stalling in 89 760T. The owner of the shop hinted that "late 80s and early 90s 760s have had problems with their computer chips" -- something like $800 plus labor -- OUCH! Has anyone heard of this?] [Response 1:] Yes, very much so...LH 2.4 modules from 1989-1991, maybe 1992 too, have been very troublesome. However, as far as I know, 1989 Turbos still used LH2.2 modules, so I'm not sure that this applies to your car. Also, often when the modules fail, they fail rather radically, such as the car running very rich, or a no-start or cases like that. [Response 2:] I experienced almost identical symptoms for several years. They went away when the ECU on my 760 Turbo had to be replaced because the AC enrichment circuit went south. [Another Opinion:] The original poster was talking about intermittent problems. That's what has me suspicious about the idea that it's the ECU. When mine died it got stuck in diagnostic mode 3, pulsing the injectors every second, which was enough fuel to start the car but not much more. Other cases I've heard of has the adaptive rich code getting set permanently. I got a rebuilt ECU from a company called Python Injection in Southern California via a place in Arizona that ordered it for me and sent it to me in Northern California. Price $400 + shipping. It's been two years and no problem so far. [Yet Another Opinion:] As a general rule, ECU's don't go half bad, and don't work intermittently: they work fine or they don't work at all. It is wires and connectors that have "off days".

Buying a Used ECU. [Suggestions:] Beware of buying one used. Generally, recyclers won't accept electronics back for exchange/refund, and any used ECU might not be much healthier than yours. You will end up paying at least 50 percent of the new price, as well, with no guarantee if it goes *poof* a week later. I know $700 is a lot of money (I also replaced mine), but caveat emptor where used stuff is concerned. I might buy something for $50 used, but $350 or more is too much unless you obtain an iron-clad return or exchange warranty of at least 30 days, and preferably 90 days.

Buying a Remanufactured ECU. Remanufactured computers are available for Asian and European cars. Two companies specialize in remanufacturing computers: Micro-Tech, in Louisville, Kentucky (800-688-1588). (sold through NAPA); and Automotive Electronics, in St. Louis (800-829-7660), a sister company of Tomco, Inc.  See also Standard Auto Parts.

760T Engine Stops Dead at 60MPH; Bad Ignition Module. [Query: driving down the highway at @ 60mph with 1/4 tank of gas in 100 degree temp in well kept 84 760 Turbo; car just dies, engine turns over but will not start] [Response:] Well, when my '84 760 Turbo died for no apparent reason as you describe, it was in the freezing dark, going over Donner Pass. Everything on the car worked except no spark and the engine wouldn't run. It turned out to be the ignition module, which is mounted on the inner driver's side fender well, above the battery, close to where someone else mentioned the ballast resistor was located. It's easy to get to and replace. If that turns out to be the culprit, shop around before buying the new part. Volvo dealers charge several hundred $$$ for this thing, but I found one from an independent parts distributor for about $90 - the identical part made by BOSCH with the same part number on it.

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