Encountering a blinking “C” on your OBD2 scanner can be perplexing, especially when you’re aiming to pass an emissions test. As a content creator for techcarusa.com and an auto repair enthusiast, I recently faced this very situation with my own Porsche 993 after a routine battery disconnection. This experience led me down a path of understanding OBDII readiness flags and the sometimes-mysterious “Catalyst Monitor,” represented by that blinking “C.”
After disconnecting my 1997 Porsche 993’s battery for maintenance, I knew resetting the car’s computer would also reset the OBDII readiness monitors. These monitors are crucial for ensuring your vehicle’s emission systems are functioning correctly and are a prerequisite for passing many state emissions tests. In Tennessee, where I live, an annual emissions test is required for registration renewal, focusing on OBDII readiness rather than a traditional “sniffer” test.
Confident from past experiences using the “BMW OBDII Drive Cycle Procedure” to set readiness indicators, I wasn’t overly concerned. I rely on an INNOVA 3100 OBDII code reader, a reliable tool I’ve used for years. My only previous issue with it was a self-inflicted error involving the immobilizer, a lesson learned the hard way.
I drove my 993 for what I estimate to be well over 1500 miles, driving it normally, including spirited drives exceeding 5000 RPM. I made no attempts to drive gently or specifically for the sake of this test, wanting to simulate real-world driving conditions.
When I finally connected my OBDII reader, I found that only three monitors were set and showing as ready:
- M – Misfire
- F – Fuel System
- CC – Comprehensive Component
However, five monitors were still in a non-ready state, indicated by a flashing display on my INNOVA 3100:
- C – Catalyst
- EV – Evaporative System
- 2A – Sec. Air System (SAI)
- O – Oxygen Sensor
- OH – Oxygen Sensor Heater
It’s worth noting that OBDII systems can support up to 11 monitors, but my Porsche 993, according to my reader and observation, utilizes only 8 of them. The blinking “C” specifically pointed to the Catalyst Monitor not being ready, which is a common hurdle after a battery disconnect.
To address these unset monitors, particularly the blinking “C”, I decided to employ the “BMW OBDII Drive Cycle Procedure.” Despite being labeled “BMW,” this procedure is often effective for various makes and models, including Porsche, due to the standardized nature of OBDII systems.
On a Saturday morning, I performed the “BMW OBDII Drive Cycle” for the first time. Throughout the drive, I kept the INNOVA 3100 reader connected to the OBDII port. This allowed me to monitor the readiness status in real-time as the reader refreshes data from the 993’s OBDII system approximately every minute. Disappointingly, after completing the drive cycle and returning home, the monitor status remained unchanged – still 3 set and 5 flashing.
After allowing the car to cool down for about four hours (in the past, I’d let it sit overnight, but I was experimenting with a shorter cool-down period this time), I attempted a second run of the drive cycle. I chose a slightly different route, but one that still allowed me to execute the “BMW OBDII Drive Cycle Procedure” steps in order. Again, the OBDII reader remained connected, constantly monitoring. Throughout this second drive, there was no change in the monitor status – the persistent 3 set and 5 flashing remained until I arrived back home.
Upon returning, I backed into my driveway and engaged the parking brake, completing the final step of the procedure: “Idle for approximately 5 minutes” (in-gear for automatic transmissions). Incredibly, after less than a minute of idling, all five remaining readiness indicators switched to a solid, non-flashing state! Success! The blinking “C” was gone, along with the flashing EV, 2A, O, and OH. All monitors were now set and ready.
It’s important to note that strictly adhering to every speed and RPM requirement of the “BMW OBDII Drive Cycle Procedure” can be challenging in real-world driving. Stop signs and corners frequently interrupt the continuous driving required for each step. I made sure to return to the specified speed and RPM as quickly as possible after any interruption. While the procedure advises against exceeding 3000 RPM or 60 MPH, I briefly exceeded these limits on two occasions, but only marginally and for very short durations. It seems these limits are guidelines rather than absolute rules, but it’s best to adhere to them as closely as possible.
This experience highlights that a blinking “C” on your OBD2 scanner, indicating a non-ready Catalyst Monitor, can often be resolved by performing a drive cycle. While the “BMW OBDII Drive Cycle Procedure” worked for my Porsche 993, similar drive cycle procedures exist for other manufacturers and can be found online or in your vehicle’s repair manual. The key is to follow the steps methodically and allow the vehicle sufficient time to run through its diagnostic routines. If you’re facing a blinking “C” and need to pass an emissions test, a drive cycle might be just the solution you need before seeking more complex or costly repairs.
