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1996 Silverado SES light Proplem

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1996 Silverado SES light Proplem

Truck Trend Truck Trend
Administrator | Posts: 4666 | Joined: 02/07
Posted: 02/10/09
05:36 PM

QUESTION: In my 1996 Silverado (with the 5.7-liter), the SES light is either on continually or it flashes intermittently. The diagnostic tool says the engine's running rich. I've changed the plugs, wires, and air filter. What usually causes this issue? The forums I've read talk about a temp-control sensor, but if it's the same one that reports the engine temperature to the instrument cluster, that works just fine.

ANSWER:  The temperature-gauge reading on the instrument panel and the coolant temperature data received by the powertrain control module (PCM) come from two different coolant temperature sensors. So whether the gauge works correctly is irrelevant to how your engine's running. Trouble codes stored in the PCM's memory indicating a rich condition don't pinpoint the cause of a problem; they alert a symptom that needs to be further diagnosed--in this case, that there's too much fuel in the air/fuel mixture. A failed oxygen sensor can incorrectly indicate a lean condition, so the PCM will unknowingly send a rich command to the fuel injectors to compensate. The same thing goes for a coolant-temperature sensor reading incorrectly low, or a stuck open thermostat actually keeping the coolant temperature below normal--the system adds more fuel accordingly. If the sensors are fine, this is a genuine rich condition, such as a failed fuel-pressure regulator leaking unwanted fuel into the intake manifold. The injectors on the CSFI fuel system have been a problem area, and fuel regulators, oxygen sensors, and mass airflow sensors are known to fail fairly often, potentially inducing a rich condition. In your case, take the truck to a hands-on technician before going any further.


If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex Steele, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 6420 Wilshire Blvd., Los Angeles, CA 90048, or e-mail us at

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