P2A59 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Intermittent/Erratic

On heavy vehicles the gas hardware sees constant shaking, and long harness runs to the vaporizers add connectors that can loosen. P2A59 records that the vaporizer B outlet signal changed faster or more erratically than real temperature can, or kept dropping out for short moments. Such faults tend to come and go with road surface, engine speed or coolant heat. The A sensor gives a good reference: if its value is smooth while B jumps, the problem is local to the B circuit. Look for green corrosion at the pins, cracked insulation and strain on the plug. No manufacturer documents P2A59; CARB still requires that sporadic faults on an input like this are detected. Expect occasional switching to petrol or a flickering gas indicator.

Likely causes

Symptoms

• Check engine light comes and goes, depending on calibration
• Sporadic switching to petrol
• Flickering gas indicator

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, law.cornell.edu, patents.google.com.