For many diagnostic techs, nothing is more discouraging and time-consuming than dealing with a no-code driveability complaint. Today’s second-generation On-Board Diagnostics II (OBD II) can be extremely sophisticated because the OBD II powertrain control modules (PCMs) in modern vehicles have far more computing capacity than did the older, pre-1996 OBD I vehicles. Nevertheless, we occasionally have to deal with a no-code performance complaint on a modern OBD II vehicle.
One of the common check engine light problems you’ll encounter on Hondas is a misfire code with no apparent misfire. Many times, this problem will be traced back to tight valve lash. Obviously, a tight valve will pass the audible test every time. But, it’s the tight valves that will set the check engine light in the best case, and if it’s ignored long enough you’ll be looking at a low-compression situation caused by a burnt valve.
You may encounter a Subaru on which the MIL flashes whenever the motor is running. There may not be any driveability complaints. The problem is that the green test mode connectors are hooked together. To diagnose the problem, locate the green single-wire test mode connectors under the driver’s side of the dash by the steering column.
This real-world case study of a 2002 Chevy S-10 pickup, a 1995 Buick and a 1995 Lincoln Town Car illustrates why “chasing” trouble codes can get you lost in the Diagnostic Woods.
Generally, when a customer brings a vehicle into a shop that has a misfire concern, they will describe it as bucking, jerking or loss of power. They also may describe it, depending on the cause, as a jerking when they take off from a start, but smoothes out once the vehicle gets moving. They may tell you the check engine light has been flashing.
Drive-by-wire throttle control systems are pretty much trouble-free but have to be taken into consideration as you perform routine service and diagnose problems, and it changes the way you service these cars when it comes to cleaning the throttle plates, advises Bob Dowie, import specialist contributor, who also covers electronic throttle control’s tie in with ABS and VSC systems.
Have you had a customer pull into the shop with a Volkswagen or Audi that just will not idle correctly? One of the possible causes is that the throttle position is not known. The ECU must know the full range of motion of the throttle in order for it to properly control the engine.
It’s a sign of the times that many people are bringing older vehicles into shops for repairs that they would not have considered several years ago. So it’s not unusual to see people spending more to repair a vehicle than its market value.
Jo was a new customer referred by an old-time regular. Her little KIA had a transmission problem that seemed to be getting the best of the transmission shop. The story goes that the SUV was constantly in limp mode, and would never shift properly … ever.
Nothing is more frustrating than diagnosing an intermittent cranking, no-start complaint with no diagnostic trouble codes (DTCs) and no apparent failure pattern. Much of the time, the cranking, no-start complaint lies with a failing crankshaft or camshaft position sensor. Many of these failures can be heat-related and might require several warm-up cycles to duplicate.
If you confirm the MIL is on with DTC U1000 (CAN COMM CIRCUIT) or DTC U1010 (CAN COMM) [2006 Models only] stored in the engine control unit, and there are no driveability incidents, determine if this bulletin applies by performing steps 1 and 2 of this Service Procedure.
You may see a tell-tale service light flashes after replacement of the ECC on 1996 and newer Saturn vehicles. When this occurs, a Crankshaft Adaptives Reset Procedure and Crankshaft Position Relearn Procedure (Flash) must be performed.