← Back to list

P1133 OBD2 Code on 1996 Blazer: Fuel/Air Monitoring Issue and Engine Power Loss

Model: 96 Blazer Fault Code: P1133 Posted: 2007-04-09 11:52

I recently purchased a 1996 Chevrolet Blazer with 135,000 miles on the odometer. Since acquisition at 125,000 miles, I've performed multiple maintenance tasks including radiator flush, transmission service, front differential repair, fuel injector cleaning, new shocks, and a fresh fuel filter. The vehicle began showing signs of reduced power early on. Initially, the radiator cap was found to be failing under pressure—after installing a new one, it held for about 100 miles before leaking again. The coolant appears mostly intact with some sludge but no significant blockages in hoses. I notice a distinct coolant burning odor when exiting the vehicle, and the engine feels overheated despite normal gauge readings. Recently, the check engine light triggered code P1133 (Fuel/Air Monitoring System Malfunction). After diagnosis at a shop, they simply turned off the light, and it has not reappeared after approximately 300 miles of driving. I now experience significant power loss—downshifting out of overdrive on hills is necessary, and in city traffic, even with full throttle, the vehicle only delivers about 50% of its expected performance. It feels as if the engine is running on fewer than six cylinders. Additionally, after warming up for 15–20 minutes, coolant spills from the radiator cap onto my battery. This behavior suggests a possible internal pressure issue in the cooling system. I plan to inspect spark plugs, EGR valve, and MAF sensor (which I believe is located on top of the engine). Any additional troubleshooting suggestions would be greatly appreciated—this vehicle is currently being considered for sale as I look to relocate. Note: The P1133 code indicates a failure in the oxygen sensor's ability to switch between rich and lean conditions, which may stem from coolant contamination in the exhaust or other combustion-related issues.

Related fault codes

P1133

Comments (6)

Anonymous 2007-04-09 11:54

I've also noticed my oil remains clean after 3000 miles of driving—no signs of contamination or degradation.

Anonymous 2007-04-09 12:05

If the radiator is spewing coolant without overheating, this could indicate combustion gases entering the cooling system. The first step should be testing for combustion gasses in the coolant using a leak detection kit (available at NAPA). A positive result may point to a failing head gasket or cylinder seal. Check compression pressure as well—this can help identify which cylinder(s) are compromised.

Anonymous 2007-04-09 14:21

If there's a bad cylinder, would I typically see coolant in my oil? I've checked the oil and don't observe any visible coolant or smell of it. This makes me wonder if combustion gasses are the real issue rather than direct coolant-oil mixing.

Anonymous 2007-04-09 14:54

Not necessarily—combustion gas leaks into coolant do not always result in coolant in oil. Head gaskets can fail in multiple ways: oil-to-coolant, coolant-to-oil, or combustion-to-coolant (less common). Combustion-to-oil is rare but possible. A small amount of coolant spewing from the cap during operation is normal if it's routed into the recovery container. If it's being expelled directly onto the battery, that indicates a problem and requires immediate inspection. The P1133 code may be related to this issue—coolant burned in the exhaust can damage oxygen sensors. This analysis is based on the symptoms described.

Anonymous 2007-04-23 15:42

I performed a combustion gas test on the radiator and found no positive results. I ran a superflush through the radiator, which removed significant rust and debris. The transmission was also serviced. I replaced all spark plugs (the truck previously ran slightly lean), and after installation, power improved somewhat—but still feels like it's only delivering about 70% of its potential. I replaced the thermostat to ensure it wasn't sticking—this reduced the coolant burning smell but not completely. The engine still runs slightly hotter than normal. I cleaned the MAF sensor with brake cleaner. The check engine light has returned, now showing code P1133 (O2 Sensor Bank 1, Sensor 1 — slow response). This sensor is located under the driver's seat, not in front of the catalytic converter. Given that this sensor is critical for fuel-air mixture control, could it be directly responsible for the power loss and performance issues I'm experiencing? I suspect a deeper underlying issue affecting both engine efficiency and emissions monitoring.

Anonymous 2007-04-23 15:49

The O2 sensor in question is on the same side of the engine as your #1 spark plug wire—have you checked your ignition coil for faults or wear? A failing coil could cause misfires, leading to poor fuel efficiency and triggering oxygen sensor errors like P1133.