The GMC Envoy four-wheel-drive (4WD) has reports and technical service bulletins (TSB) about problems with the electronic control unit (ECU). The ECU controls the timing of the engine, the fuel-injection system and the idle control, and controls the power that goes to the fuel injectors as well as to many other engine components. These ECU issues can create multiple symptoms, or just one symptom, which will affect the efficiency of the Envoy engine.
The Envoy 4WD has a TSB published from the manufacturer about corrosion problems on the ECU causing fault lights to illuminate when there are no problems. The debris and chemicals from the road are contaminating the ECU and causing corrosion to build up on the control unit. This corrosion problem with the ECU causes fault lights or warning lights on the instrument panel to illuminate incorrectly, which misinforms the Envoy operator that there is a problem. Warning lights such as those pertaining to electrical concerns and instrument panel gauges, however, become inoperative because of this ECU problem on the Envoy.
One TSB published on the Envoy 4WD states that there is a problem with the engine losing power. The ECU is not sending the proper signals to the power control or the fuel injectors, causing the engine to lose power during normal driving conditions. The Envoy engine will begin to stall or hesitate during acceleration. No specific reason is given for this ECU problem, with the exception of a programming problem with the control unit. The Envoy owner needs to take the SUV into the dealership and have the ECU reprogrammed in order to ensure that the signals sent to the power control or the fuel injectors are activated.
The ECU on the Envoy 4WD controls the fuel injectors and the times when the injectors are fired in order for the engine to run efficiently, according to one of the TSBs published on the GMC vehicle. But the fuel injectors can get clogged from excessive debris coming through the fuel filter, and the ECU will not recognize that the fuel injectors have a problem. The Envoy will begin to take a long time to start, idle speed will be reduced and not be controlled by the ECU, and the engine will begin to misfire when the ECU is not controlling everything properly -- not to mention the injectors being clogged. If this ECU problem continues and the Envoy is driven with clogged fuel injectors, the Envoy engine will begin to overheat and then fail. Once these symptoms develop, the fuel injectors need to be cleaned and the ECU needs to be reprogrammed by the dealership.
