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sprinkles08, ASE Certified Technician
Category: Chevy
Satisfied Customers: 23129
Experience:  ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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1990 Chevy truck runs ruff code 34 map signal low during ignition

Customer Question

1990 Chevy truck runs ruff code 34 map signal low during ignition on
Submitted: 2 years ago.
Category: Chevy
Expert:  sprinkles08 replied 2 years ago.
Hello and welcome to JustAnswer!
Code 34 sets when the MAP signal voltage falls too low with the engine running. This could be a couple things and it will take some electrical testing to know exactly what is going on.
It could be a short to ground on the MAP sensor signal circuit between the sensor and engine controller. The signal circuit should be tested for a short to ground as well as making sure the 5v reference is present with the key on and sensor unplugged.
If the reference and signal wire are ok then the issue is going to be the sensor itself. A failed engine controller could potentially set the code but it would be very unlikely.
Customer: replied 2 years ago.
How do I do this test
Expert:  sprinkles08 replied 2 years ago.
A digital voltmeter is needed.