Under the Hood

7 Uncommon OBD-II Codes & What They Mean

March 29, 2019

Who’s down with OBD? Yeah, you know: Me!

When DIY mechanics troubleshoot a car problem, they rely on experience, their guts, and what their code scanners spit out. But what do all those OBD-II codes mean? With help from some friendly Kansas City service technicians at McCarthy, here are 7 of the most uncommon OBD2 diagnostic errors they’ve encountered, plus a list of symptoms, causes, and potential fixes for each.

#7) P00B7 – Engine Coolant Flow Performance

What it means: Engine’s internal computing system has detected instability in coolant temperatures (typically high temperatures).

Common symptoms: Engine Service Light • Overheating • Sputtering Engine • Heater Not Working

Potential causes: Low Coolant Level • Faulty Coolant Reservoir • Failing Thermostat • Bad Head Gasket • Coolant Leak

Needed repairs: Depending on the symptom, the following repairs may be necessary to fix P00B7 codes:

  • Replace coolant reservoir cap
  • Replace recovery tank and coolant reservoir
  • Install new thermostat
  • Replace head gasket
  • Replace radiator
  • Add coolant (after a fluid flush)
  • Investigate for air pockets in cooling lines

#6) P0460 – Fuel Level Sensor

What it means: The PCM has detected an unusual signal from the fuel level sensor, which tells drivers how much fuel is in the tank.

Common symptoms: Wildly Inaccurate Fuel Gauge Readings

Potential causes: Failing Fuel Pump • Poor Wiring • Faulty Fuel Level Sensor • Bad Flex Fuel Module (certain models)

Needed repairs: Annoying though not essential to fix, bad fuel level sensors are usually due to either a faulty sensor or loose/damaged wiring within the dash.

#5) P0316 – Engine Misfire Detected on Startup

What it means: The engine control monitor has found that cylinders are not working to ensure the engine is running as intended, resulting in misfires.

Common symptoms: Poor Performance • Bad Fuel Economy • Check Engine Light • Rough Idling • Shaky Driving

Potential causes: Failed Spark Plugs • Defective Fuel Injector • Bad Ignition Coil • Engine Failure • Loose Spark Plug Wires

Needed repairs: Typically, changing spark plugs or tightening spark plug wires will resolve P0316 codes. However, if damage has occurred to any part of the fuel injector or ignition coil system, they will need to be replaces, as will any related system component.

#4) P037D/E/F – Glow Plug Sense Circuit

What it means: In diesel engines, glow plugs aid in cold engine starts by heating up combustion chambers. If the circuit to the glow plugs fail, the PCM will send P037D/E/F codes.

Common symptoms: Engine Won’t Start • Engine is Difficult to Start • Vehicle Won’t Turn Over in Cold

Potential causes: Bad Glow Plug Control Modules • Failed Glow Plugs • PCM Failure • Loose or Damaged Wiring

Needed repairs: A simple glow plug replacement solves the majority of P037 codes, though you’ll want to search for signs of damaged wiring or a faulty control module.

#3) P0130 – Oxygen Sensor Malfunction

What it means: Voltage or air-fuel ratio of your O2 sensor is too low, or your oxygen sensor is failing to measure exhaust data accurately.

Common symptoms: Check Engine Light • Rough Idling • Poor MPGs • Dark Exhaust or No Exhaust • Loud Noises at High Speeds • Carbon Monoxide Leaks in Cabin (!)

Potential causes: Defective O2 Sensor or Circuit • Leak in Exhaust or Intake Air System • Bad PCM Software • Low Fuel Pressure

Needed repairs: Replacing the O2 sensor is the most common P0130 repair, and something a novice mechanic may be able to do. However, other P0130 fixes may include:

  • Install new high-pressure fuel pump
  • Inspect for shorted wires and electrical connectors
  • Check for faulty upstream (sensor 1)/downstream (sensor2) data
  • Install new catalytic converter
  • Replace oxygen sensor harness

#2) P0526 – Fan Speed Sensor Circuit

What it means: The engine control module cannot correctly or adequately control the vehicle’s electric cooling fan system.

Common symptoms: Nonfunctioning A/C • Cooling Fans Always On/Off • Overheating Engine

Potential causes: Failing Engine Cooling Fan Control Module • Relay Failure • Seized Fans • Loose Wires

Needed repairs: To fix P0526 problems, the car’s fan speed sensor should be inspected and replaced, and a new radiator fan assembly should be installed.

#1) P0635 – Power Steering Control Circuit

What it means: A defect in the charging system, relative to the power steering control unit, has been detected.

Common symptoms: Battery Charging Warning Light • Electronics Automatically Disabled • Random Loss of Power Steering • Battery Does Not Hold Charge

Potential causes: Bad Alternator • Faulty Power Steering System • Broken Pulleys • Corrosion

Needed repairs: Any issue with the internal charging system is commonly caused by a bad alternator, though a defective power steering control circuit could be the culprit if the only symptom is a loss of power steering. In that instance, you should bring your vehicle to a service center right away, as driving with a bad power steering system is very dangerous.

Have any weird OBD2 codes that you’ve encountered? Drop me a comment — I’m dying to know what the problem and solution was!


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