The oil pressure sensor in the '84-87 A/C-equipped Fiero is prone to problems. There is a vent hole in the sensor which allows entry of water and humid air. Over time, the internals of the sensor corrode and cause an erratic oil pressure gauge or complete failure. A GM Techincal Service Bulletin advises to plug the sensor hole and use a rubber cap over the connector. The GM part number for the plug is 12085529. A dab of silicone will serve the same purpose. The electrical connector, should you need to replace it, is part number 12085529.
If you want to see what the inside of a damaged oil pressure sensor looks like, check this link: Damaged Sensor
The damage-prone sensor in the '84-87 Fiero can be replaced by the sensor from an '88 Fiero but requires a matching connector. Some replacement sensors for the '88 Fiero may come with 4 electrical pins in the socket, but only three of the pins are used in the Fiero wiring. If you use one of the 4-pin replacement sensors in an earlier Fiero, be sure to correctly wire the mating connector!
Another "feature" of the oil pressure sensor (all years) is it contains contacts which supply power to the fuel pump after oil pressure has been established. However these contacts are in parallel with two contacts in the fuel pump relay which also provides power to the fuel pump. If the fuel pump relay fails all the power for the pump goes through the contacts in the oil pressure sensor. Apparently these contacts are not rated for the full pump load. This can cause the contacts to overheat and damage the pressure-sensing portion of the sensor. We believe GM erred in this application. The sensor as described by AC Delco (the sensor manufacurer) is for "oil pressure w/light". It appears the contacts within the switch were intended for an "idiot light" on the dash, not as current-carrying components for the fuel pump. Therefore, running fuel pump power through the sensor seems to be a design error, but that's the way it is (unless you change it).
The oil pressure sensor in the '88 Fiero is a different design (no vent hole) but still has the contacts for the fuel pump. If your oil pressure gauge always reads maximum pressure the culprit is likely (a) the fuel pump relay has failed and therefore all current for the fuel pump is going through the oil pressure sensor, and (b) the oil pressure sensor has subsequently overheated and the pressure-sensing portion of the unit has short-circuited, thus giving a high gauge reading. It is wise to check the fuel pump relay when the oil pressure sensor is replaced.
If you purchase a new sensor, the GM part numbers are as follows:
'84 - #25036378 (AC Delco D1816) '85-87 - #10045775 (AC Delco D1808) '88 - #12555492 (was #10096169 in the 22P manual) (AC Delco D1808A)
A new oil pressure sensor runs $25-50 depending on where you shop. However, be careful what you purchase. There are Taiwanese oil pressure sensors sold as replacements for the V-6 ('85-'88, even though the '88 is different) which are definitely mis-wired internally. They will cause the gauge fuse to blow, the oil pressure gauge to peg, and the fuel pump will not run initially when the ignition is turned to "ON". These sensors come as different brands and in different boxes but all are made in Taiwan. We suggest you try AC Delco sensors and keep the receipt!
'84 Fiero: The vehicles listed below used the same oil pressure sensor as the '84 Fiero, GM Part No. 25036378. This is the same as AC Delco D1816. If you search the AC Delco site, part D1816 is available but is not listed for ANY vehicle. If you search AC Delco for the '84 Fiero oil pressure sensor you will get Part No. F1808 which is the same as the '85-87 Fiero.
'85-88 Chevy S10 Blazer Base, 4 Cyl 2.5L VIN E '85-86 Chevy S10 Blazer Durango, 4 Cyl 2.5L VIN E '87-88 Chevy S10 Blazer High Country, 4 Cyl 2.5L VIN E '85-88 Chevy S10 Blazer Sport, 4 Cyl 2.5L VIN E '85-88 Chevy S10 Blazer Tahoe, 4 Cyl 2.5L VIN E
'87-88 Buick Century Custom V6 3.8L 231cid VIN 3 '87-88 Buick Century Estate Wagon V6 3.8L 231cid VIN 3 '87-88 Buick Century Limited V6 3.8L 231cid VIN 3 '86 Buick Electra V6 3.8L 231cid VIN B '86 Buick Electra Park Avenue V6 3.8L 231cid VIN B '86 Buick Electra T-Type V6 3.8L 231cid VIN B '86 Buick LeSabre Custom V6 3.0L 181cid VIN 3, B, L '86 Buick LeSabre Limited V6 3.0L 181cid VIN 3, L '84 Buick Skyhawk Custom L4 1.8L 112cid VIN J '82-86 Buick Skyhawk Custom/Limited L4 1.8L 112cid VIN 0 '86 Buick Skyhawk Sport L4 1.8L 112cid VIN O '83-86 Buick Skyhawk T-Type L4 1.8L 112cid VIN 0 '84-86 Buick Skyhawk T-Type L4 1.8L 112cid VIN J '84 Buick Skylark Custom/Limited L4 2.5L 2474cc 151cid VIN R '86 Buick Skylark Custom/Limited L4 2.5L 2474cc 151cid VIN U '86 Buick Skylark Custom/Limited V6 3.0L 181cid VIN L '85 Buick Somerset Regal/Limited L4 2.5L 2474cc 151cid VIN U '86 Buick Somerset/Limited/T-Type L4 2.5L 2474cc 151cid VIN U '86 Buick Somerset/Limited V6 3.0L 181cid VIN L '85 Buick Somerset Regal/Limited V6 3.0L 181cid VIN L '86 Buick Somerset T-Type V6 3.0L 181cid VIN L '85-88 Chevrolet Astro L4 2.5L 2474cc 151cid VIN E '84-86 Chevrolet Camaro L4 2.5L 2474cc 151cid VIN 2 '83 Chevrolet Citation L4 2.5L 2474cc 151cid VIN 5 '83-85 Chevrolet Citation L4 2.5L 2474cc 151cid VIN R '87-91 Chevrolet LLV (Postal Vehic.) L4 2.5L 2474cc 151cid VIN A '91 Chevrolet LLV (Postal Vehic.) L4 2.5L 2474cc 151cid VIN E '85-86 Chevrolet S10 Blazer/Pickup L4 2.5L 2474cc 151cid VIN E '85-86 GMC S15 Jimmy/Pickup L4 2.5L 2474cc 151cid VIN E '85-88 GMC Safari L4 2.5L 2474cc 151cid VIN E '86 Oldsmobile 98 Regency/Brougham V6 3.8L 231cid VIN B '85-86 Oldsmobile Calais L4 2.5L 2474cc 151cid VIN U '85-86 Oldsmobile Calais V6 3.0L 181cid VIN L '85-86 Oldsmobile Calais Supreme L4 2.5L 2474cc 151cid VIN U '85-86 Oldsmobile Calais Supreme V6 3.0L 181cid VIN L '85-90 Oldsmobile Cutlass Ciera L4 2.5L 2474cc 151cid VIN R '86-88 Oldsmobile Cutlass Ciera V6 3.8L 231cid VIN 3 '84-88 Oldsmobile Cutlass Ciera Brougham L4 2.5L 2474cc 151cid VIN R '87-88 Oldsmobile Cutlass Ciera Brougham V6 3.8L 231cid VIN 3 '84-90 Oldsmobile Cutlass Ciera Cruiser L4 2.5L 2474cc 151cid VIN R '87-88 Oldsmobile Cutlass Ciera Cruiser V6 3.8L 231cid VIN 3 '87-88 Oldsmobile Cutlass Ciera Cruiser Brougham L4 2.5L 2474cc 151cid VIN R '87-88 Oldsmobile Cutlass Ciera Cruiser Brougham V6 3.8L 231cid VIN 3 '89 Oldsmobile Cutlass Ciera Cruiser SL L4 2.5L 2474cc 151cid VIN R '88 Oldsmobile Cutlass Ciera Internat. V6 3.8L 231cid VIN 3 '84-85 Oldsmobile Cutlass Ciera LS L4 2.5L 2474cc 151cid VIN R '87 Oldsmobile Cutlass Ciera S L4 2.5L 2474cc 151cid VIN R '87 Oldsmobile Cutlass Ciera S V6 3.8L 231cid VIN 3 '90 Oldsmobile Cutlass Ciera S L4 2.5L 2474cc 151cid VIN R '87-89 Oldsmobile Cutlass Ciera SL L4 2.5L 2474cc 151cid VIN R '87-88 Oldsmobile Cutlass Ciera SL V6 3.8L 231cid VIN 3 '86 Oldsmobile Delta 88 Royale V6 3.0L 181cid VIN L '86 Oldsmobile Delta 88 Royale V6 3.8L 231cid VIN 3 '86 Oldsmobile Delta 88 Royale Brougham V6 3.0L 181cid VIN L '86 Oldsmobile Delta 88 Royale Brougham V6 3.8L 231cid VIN 3 '82 Oldsmobile Firenza/LX/S/SX L4 1.8L 112cid VIN G '82-86 Oldsmobile Firenza/LX/S/SX L4 1.8L 112cid VIN 0 '86 Oldsmobile Firenza LC L4 1.8L 112cid VIN 0 '82-85 Oldsmobile Firenza SX L4 1.8L 112cid VIN 0 '84 Oldsmobile Omega/Brougham L4 2.5L 2474cc 151cid VIN R '84-88 Pontiac 6000 L4 2.5L 2474cc 151cid VIN R '84-90 Pontiac 6000 LE L4 2.5L 2474cc 151cid VIN R '85-87 Pontiac Fiero GT/Fiero SE V6 2.8L 173cid VIN 9 '85-87 Pontiac Fiero/Fiero SE L4 2.5L 2474cc 151cid VIN R '84-86 Pontiac Firebird/ Firebird SE L4 2.5L 2474cc 151cid VIN 2 '85-86 Pontiac Grand Am L4 2.5L 2474cc 151cid VIN U '85-86 Pontiac Grand Am V6 3.0L 181cid VIN L '85-86 Pontiac Grand Am LE L4 2.5L 2474cc 151cid VIN U '85-86 Pontiac Grand Am LE V6 3.0L 181cid VIN L '86 Pontiac Grand Am SE V6 3.0L 181cid VIN L '82-83 Pontiac J2000 L4 1.8L 112cid VIN 0 '84 Pontiac J2000 Sunbird L4 1.8L 112cid VIN 0 or J '84 Pontiac J2000 Sunbird LE L4 1.8L 112cid VIN 0 or J '84 Pontiac J2000 Sunbird SE L4 1.8L 112cid VIN J '83-84 Pontiac Phoenix L4 2.5L 2474cc 151cid VIN R '84 Pontiac Phoenix LE L4 2.5L 2474cc 151cid VIN R '83 Pontiac Phoenix LJ L4 2.5L 2474cc 151cid VIN R '85-86 Pontiac Sunbird L4 1.8L 112cid VIN O or J '86 Pontiac Sunbird GT L4 1.8L 112cid VIN 0 or J '85 Pontiac Sunbird LE L4 1.8L 112cid VIN 0 or J '85-86 Pontiac Sunbird SE L4 1.8L 112cid VIN J '86 Pontiac Sunbird SE L4 1.8L 112cid VIN 0
'87 Buick Electra Limited V6 3.8L 231cid VIN 3 '88-89 Buick Electra Limited V6 3.8L 231cid VIN C '87 Buick Electra Park Avenue V6 3.8L 231cid VIN 3 '88-89 Buick Electra Park Avenue V6 3.8L 231cid VIN C '87 Buick Electra T-Type V6 3.8L 231cid VIN 3 '88-89 Buick Electra T-Type V6 3.8L 231cid VIN C '89 Buick Electra Ultra V6 3.8L 231cid VIN C '87-90 Buick LeSabre V6 3.8L 231cid VIN 3 or C '87-90 Buick LeSabre Custom V6 3.8L 231cid VIN 3 or C '87-90 Buick LeSabre Limited V6 3.8L 231cid VIN 3 or C '91-94 Buick Regal Custom V6 3.1L 189cid VIN T or M '91-93 Buick Regal Limited V6 3.1L 189cid VIN T '88-89 Buick Skyhawk L4 2.0L 122cid VIN 1 or K '87 Buick Skyhawk Custom L4 2.0L 122cid VIN 1, K or M '87 Buick Skyhawk Limited L4 2.0L 122cid VIN 1, K or M '87 Buick Skyhawk Sport L4 2.0L 122cid VIN 1, K or M '90 Buick Skylark L4 2.5L 151cid VIN U '87-88 Buick Skylark Custom V6 3.0L 181cid VIN L '87-89 Buick Skylark Custom L4 2.5L 151cid VIN U '94-95 Buick Skylark Custom V6 3.1L 189cid VIN M '90 Buick Skylark Gran Sport L4 2.5L 151cid VIN U '94-95 Buick Skylark Gran Sport V6 3.1L 189cid VIN M '87-88 Buick Skylark Limited L4 2.5L 151cid VIN U '87-88 Buick Skylark Limited V6 3.0L 181cid VIN L '94-95 Buick Skylark Limited V6 3.1L 189cid VIN M '90 Buick Skylark Luxury Edition L4 2.5L 151cid VIN U '87 Buick Somerset L4 2.5L 151cid VIN U '87 Buick Somerset V6 3.0L 181cid VIN L '87 Buick Somerset Limited L4 2.5L 151cid VIN U '87 Buick Somerset Limited V6 3.0L 181cid VIN L '85 Chevrolet Astro V6 4.3L 262cid VIN N '85-90 Chevrolet Astro L4 2.5L 151cid VIN E '86-90 Chevrolet Astro V6 4.3L 262cid VIN Z '90 Chevrolet Astro V6 4.3L 262cid VIN B '88-89 Chevrolet Beretta L4 2.0L 122cid VIN 1 '90-91 Chevrolet Beretta L4 2.2L 134cid VIN G '90-93 Chevrolet Beretta V6 3.1L 189cid VIN T '92-93 Chevrolet Beretta L4 2.2L 134cid VIN 4 '94-96 Chevrolet Beretta V6 3.1L 189cid VIN M '90-93 Chevrolet Beretta GT V6 3.1L 189cid VIN T '92-93 Chevrolet Beretta GT L4 2.2L 134cid VIN 4 '91-93 Chevrolet Beretta GTZ V6 3.1L 189cid VIN T '94-96 Chevrolet Beretta Z26 V6 3.1L 189cid VIN M '94 Chevrolet Blazer V8 6.5L 395cid Diesel VIN S '93-94 Chevrolet Camaro V6 3.4L 207cid VIN S '88-89 Chevrolet Cavalier L4 2.0L 122cid VIN 1 '90 Chevrolet Cavalier L4 2.2L 134cid VIN G '90 Chevrolet Cavalier V6 3.1L 189cid VIN T '88 Chevrolet Cavalier RS L4 2.0L 122cid VIN 1 '91 Chevrolet Cavalier RS L4 2.2L 134cid VIN G '91-94 Chevrolet Cavalier RS V6 3.1L 189cid VIN T '92-94 Chevrolet Cavalier RS L4 2.2L 134cid VIN 4 '88 Chevrolet Cavalier VL L4 2.0L 122cid VIN 1 '90 Chevrolet Cavalier VL L4 2.2L 134cid VIN G '91-94 Chevrolet Cavalier VL L4 2.2L 134cid VIN G or 4 '90-94 Chevrolet Cavalier Z24 V6 3.1L 189cid VIN T '88-89 Chevrolet Corsica L4 2.0L 122cid VIN 1 '94-96 Chevrolet Corsica V6 3.1L 189cid VIN M '90-91 Chevrolet Corsica LT L4 2.2L 134cid VIN G '90-93 Chevrolet Corsica LT V6 3.1L 189cid VIN T '92-93 Chevrolet Corsica LT L4 2.2L 134cid VIN 4 '90 Chevrolet Corsica LTZ V6 3.1L 189cid VIN T '90-95 Chevrolet Corvette ZR-1 V8 5.7L 350cid VIN J '87-90 Chevrolet LLV (postal vehicle) L4 2.5L 151cid VIN E '90-92 Chevrolet Lumina L4 2.5L 151cid VIN R '91-92 Chevrolet Lumina V6 3.1L 189cid VIN T '91-92 Chevrolet Lumina APV V6 3.1L 189cid VIN D '92 Chevrolet Lumina Euro V6 3.1L 189cid VIN T '92 Chevrolet Lumina Euro V6 3.4L 207cid VIN X '91 Chevrolet Lumina Euro+C134 V6 3.1L 189cid VIN T '91-92 Chevrolet Lumina Z34 V6 3.4L 207cid VIN X '95 Chevrolet P30 Van V8 5.7L 350cid VIN K or R '95-96 Chevrolet P30 Van V6 4.3L 262cid VIN W or Z '95-96 Chevrolet P30 Van V8 7.4L 454cid VIN J or N '89-90 Chevrolet S10 Pickup L4 2.5L 151cid VIN E '90 GMC Safari XT V6 4.3L 262cid VIN Z '85 GMC Safari L4 2.5L 151cid VIN E '85 GMC Safari V6 4.3L 262cid VIN N '86-87 GMC Safari V6 4.3L 262cid VIN Z '86-90 GMC Safari L4 2.5L 151cid VIN E '88-90 GMC Safari V6 4.3L 262cid VIN Z '90 GMC Safari V6 4.3L 262cid VIN B '89-90 GMC S15 Pickup L4 2.5L 151cid VIN E '97 GMC MD Bus Chassis V8 6.5L 395cid VIN F '97 GMC Low Cab Forward V8 6.5L 395cid VIN F '87-89 Oldsmobile 98 Regency V6 3.8L 231cid VIN 3 '87 Oldsmobile 98 Regency Brougham V6 3.8L 231cid VIN 3 '88-89 Oldsmobile 98 Regency Brougham V6 3.8L 231cid VIN C '88-89 Oldsmobile 98 Regency Touring V6 3.8L 231cid VIN C '94-95 Oldsmobile Achieva S V6 3.1L 189cid VIN M '94 Oldsmobile Achieva SC V6 3.1L 189cid VIN M '94-95 Oldsmobile Achieva SL V6 3.1L 189cid VIN M '87 Oldsmobile Calais L4 2.5L 151cid VIN U '87 Oldsmobile Calais V6 3.0L 181cid VIN L '87 Oldsmobile Calais Supreme L4 2.5L 151cid VIN U '87 Oldsmobile Calais Supreme V6 3.0L 181cid VIN L '88 Oldsmobile Cutlass Calais V6 3.0L 181cid VIN L '88-91 Oldsmobile Cutlass Calais L4 2.5L 151cid VIN U '89 Oldsmobile Cutlass Calais S V6 3.3L 204cid VIN N '89-91 Oldsmobile Cutlass Calais S L4 2.5L 151cid VIN U '88 Oldsmobile Cutlass Calais SL V6 3.0L 181cid VIN L '88-89 Oldsmobile Cutlass Calais SL L4 2.5L 151cid VIN U '89-91 Oldsmobile Cutlass Calais SL V6 3.3L 204cid VIN N '89-91 Oldsmobile Cutlass Ciera V6 3.3L 204cid VIN N '91-92 Oldsmobile Cutlass Ciera L4 2.5L 151cid VIN R '89 Oldsmobile Cutlass Ciera Cruiser V6 3.3L 204cid VIN N '90 Oldsmobile Cutlass Ciera Cruiser V6 3.3L 204cid VIN N '91 Oldsmobile Cutlass Ciera Cruiser S V6 3.3L 204cid VIN N '91-92 Oldsmobile Cutlass Ciera Cruiser S L4 2.5L 151cid VIN R '89-91 Oldsmobile Cutlass Ciera Cruiser SL V6 3.3L 204cid VIN N '89-90 Oldsmobile Cutlass Ciera Internat V6 3.3L 204cid VIN N '90-91 Oldsmobile Cutlass Ciera S V6 3.3L 204cid VIN N '91 Oldsmobile Cutlass Ciera S L4 2.5L 151cid VIN R '89-91 Oldsmobile Cutlass Ciera SL V6 3.3L 204cid VIN N '91 Oldsmobile Cutlass Supreme V6 3.4L 207cid VIN X '91-92 Oldsmobile Cutlass Supreme V6 3.1L 189cid VIN T '91-92 Oldsmobile Cutlass Supreme Inernat V6 3.1L 189cid VIN T '91-92 Oldsmobile Cutlass Supreme Inernat V6 3.4L 207cid VIN X '92 Oldsmobile Cutlass Supreme S V6 3.1L 189cid VIN T '92 Oldsmobile Cutlass Supreme S V6 3.4L 207cid VIN X '91 Oldsmobile Cutlass Supreme SL V6 3.1L 189cid VIN T '91 Oldsmobile Cutlass Supreme SL V6 3.4L 207cid VIN X '87-88 Oldsmobile Delta 88 Royale V6 3.8L 231cid VIN 3 '88-90 Oldsmobile Delta 88 Royale V6 3.8L 231cid VIN C '87-88 Oldsmobile Delta 88 Royale Brougham V6 3.8L 231cid VIN 3 '88-90 Oldsmobile Delta 88 Royale Brougham V6 3.8L 231cid VIN C '87-88 Oldsmobile Firenza L4 2.0L 122cid VIN K '88 Oldsmobile Firenza L4 2.0L 121cid VIN 1 '87 Oldsmobile Firenza LC L4 2.0L 122cid VIN K '87 Oldsmobile Firenza LX L4 2.0L 122cid VIN K '87 Oldsmobile Firenza S L4 2.0L 122cid VIN K '91-92 Oldsmobile Silhouette V6 3.1L 189cid VIN D '91 Pontiac 6000 LE L4 2.5L 151cid VIN R '91 Pontiac 6000 LE/SE V6 3.1L 189cid VIN T '87 Pontiac Bonneville V6 3.8L 231cid VIN 3 '87-88 Pontiac Bonneville LE V6 3.8L 231cid VIN 3 '88-90 Pontiac Bonneville LE V6 3.8L 231cid VIN C '88-89 Pontiac Bonneville SE V6 3.8L 231cid VIN C '88 Pontiac Fiero L4 2.5L 151cid VIN R '88 Pontiac Fiero/Fiero GT V6 2.8L 173cid VIN 9 '93-94 Pontiac Firebird V6 3.4L 207cid VIN S '87 Pontiac Grand Am V6 3.0L 181cid VIN L '87-88 Pontiac Grand Am L4 2.5L 151cid VIN U '94-95 Pontiac Grand Am GT V6 3.1L 189cid VIN M '87 Pontiac Grand Am LE V6 3.0L 181cid VIN L '87-88 Pontiac Grand Am LE L4 2.0L 122cid VIN M '87-90 Pontiac Grand Am LE L4 2.5L 151cid VIN U '87 Pontiac Grand Am SE L4 2.5L 151cid VIN U '87 Pontiac Grand Am SE V6 3.0L 181cid VIN L '87-89 Pontiac Grand Am SE L4 2.0L 122cid VIN M '94-94 Pontiac Grand Am SE V6 3.1L 189cid VIN M '92 Pontiac Grand Prix V6 3.4L 207cid VIN X '91-92 Pontiac Grand Prix GT V6 3.1L 189cid VIN T '91-92 Pontiac Grand Prix GT V6 3.4L 207cid VIN X '91-92 Pontiac Grand Prix LE V6 3.1L 189cid VIN T '92 Pontiac Grand Prix LE V6 3.4L 207cid VIN X '91-92 Pontiac Grand Prix SE V6 3.1L 189cid VIN T '91-92 Pontiac Grand Prix SE V6 3.4L 207cid VIN X '91-92 Pontiac Grand Prix STE V6 3.1L 189cid VIN T '91-92 Pontiac Grand Prix STE V6 3.4L 207cid VIN X '87-88 Pontiac Sunbird L4 2.0L 122cid VIN K '91 Pontiac Sunbird L4 2.0L 122cid VIN K '94 Pontiac Sunbird V6 3.1L 189cid VIN T '87-90 Pontiac Sunbird GT L4 2.0L 122cid VIN K or M '91-93 Pontiac Sunbird GT V6 3.1L 189cid VIN T '89-91 Pontiac Sunbird LE L4 2.0L 122cid VIN K '90 Pontiac Sunbird LE L4 2.0L 122cid VIN M '91 Pontiac Sunbird LE V6 3.1L 189cid VIN T '92-93 Pontiac Sunbird LE L4 2.0L 122cid VIN H '93-94 Pontiac Sunbird LE V6 3.1L 189cid VIN T '87-89 Pontiac Sunbird SE L4 2.0L 122cid VIN M '87-91 Pontiac Sunbird SE L4 2.0L 122cid VIN K '91-94 Pontiac Sunbird SE V6 3.1L 189cid VIN T '92-93 Pontiac Sunbird SE L4 2.0L 122cid VIN H '91-92 Pontiac Trans Sport V6 3.1L 189cid VIN D