During this same week, Pratt and Whitney Aircraft tested a LEM-type fuel cell for 400 hours without shutdown and reported no leaks.
At 8:13 p.m. EST a 217-second S-IVB auxiliary propulsion system burn aimed the S-IVB for a lunar target point so accurately that another burn was not required. The S-IVB/IU impacted the lunar surface at 8:10 p.m. EST on April 14 at a speed of 259 meters per second. Impact was 137.1 kilometers from the Apollo 12 seismometer. The seismic signal generated by the impact lasted 3 hours 20 minutes and was so strong that a ground command was necessary to reduce seismometer gain and keep the recording on the scale. The suprathermal ion detector experiment, also deployed by the Apollo 12 crew, recorded a jump in the number of ions from zero at the time of impact up to 2,500 shortly thereafter and then back to a zero count. Scientists theorized that ionization had been produced by 6,300 K to 10,300 K (6,000 degrees C to 10,000 degrees C) temperature generated by the impact or that particles had reached an altitude of 60 kilometers from the lunar surface and had been ionized by sunlight.
Meanwhile back in the CSM/LM, the crew had been performing the routine housekeeping duties associated with the period of the translunar coast. At 30:40 ground elapsed time a midcourse correction maneuver took the spacecraft off a free-return trajectory in order to control the arrival time at the moon. Ensuring proper lighting conditions at the landing site. The maneuver placed the spacecraft on the desired trajectory, on which the closest approach to the moon would be 114.9 kilometers.
At 10:08 p.m. EST April 13, the crew reported an undervoltage alarm on the CSM main bus B, rapid loss of pressure in SM oxygen tank No. 2, and dropping current in fuel cells 1 and 3 to a zero reading. The loss of oxygen and primary power in the service module required an immediate abort of the mission. The astronauts powered up the LM, powered down the CSM, and used the LM systems for power and life support. The first maneuver following the abort decision was made with the descent propulsion system to place the spacecraft back in a free-return trajectory around the moon. After the spacecraft swung around the moon, another maneuver reduced the coast time back to earth and moved the landing point from the Indian Ocean to the South Pacific.